Another little piece just popped out at me.
I theorized in "I Would Sell Out the Nation" that the explicit, and to wizards mortally-terrifying, crime inherent in becoming a DE was swearing oneself to the revocation of Secrecy - the worst and most heretically-inflected form of treason possible in the WW. All but unthinkable to any sane or decent witch or wizard, and very rarely spoken of directly. And that it was the Ministry's and then the public's discovery of this fact about Voldemort's organization, right when he seemed to be poised for a takeover, that prompted Crouch's Unforgivables policy.
Might that same discovery by the Ministry also explain another curious little mystery we never got a satisfying answer for?
Exactly how, when, and why did Voldemort make himself unmentionable? The first time around - before he got control of the Ministry and its various tracking apparatuses in DH.
Um.
Perhaps we should be asking: DID he? By some unknown direct and deliberate action of his own, that is? One that we just happen to never have had described for us in its mechanism or effects...
Or is this another clue?
Item: we are never told what precisely Voldemort's supposed goal in making himself unmentionable back in VWI might have been, how this might supposedly have helped him then, precisely when he did so, or how he managed it logistically/magically. Only that sometime in the late stages of the war, around when Crouch altered his policy, Voldemort made himself terrifying enough that the wizarding public was afraid to say his name, and resorted superstitiously to clumsy circumlocutions that most non-Order witches and wizards still prefer to use even while he is known to be gone. Dumbledore and some of his known longstanding followers, however, make a point of using the name 'Voldemort' to highlight their bravery in their commitment to fighting against him.
Item: Dumbledore's Order was always extra-legal, but included Ministry personnel among its longtime members; was by purpose anti-Voldemort like Dumbledore himself publicly was, while being inclusive of muggleborn and unusually-muggle-interested members; and was at times viewed with some suspicion by the Ministry (and viewed it with occasional suspicion in return) but was generally allied with it and never directly targetted by it until Voldemort's takeover.
Item: the only people we consistently see or hear of ever using the name 'Lord Voldemort' and its variants are, first, the old group of followers from school he first started using the name among, and then later - after Dumbledore learned of it - Dumbledore and his followers, pointedly. When we hear of Death Eaters, specifically, using the new title - and general historical category descriptor - 'the Dark Lord' in reference to their master, while showing fear of using his old name or being present when that name is spoken. Even while within the confines of Dumbledore's own stronghold at Hogwarts, Dumbledore's pet DE spy - released by closed hearing and not known even to Fudge as a DE - vehemently smacks down mention of the name in his presence.
Item: even among Dumbledore's followers, as well as the public, in the interwar years and the second war, there is a curious trend to discuss Voldemort and the DEs' program in vague terms, combining indications of his goal to 'take over' and rule the WW and muggles with descriptions of anti-muggle or blood-prejudice-related thinking and action, while leaving any mention of the most massive necessary EFFECT of his attempt at direct muggle rule - the ending of Secrecy - to be present but generally implicit or circumlocuted. Rarely if ever directly stated, and never discussed itself in explicit detail as such for long.
Item: once known, the heretical and treasonous - because anti-Secrecy - cause to which the Death Eaters had committed themselves was so terrifying to the wizarding public that they supported a Ministry program of extra-judicial torture and execution of even suspected Death Eaters. While also being terrified of how difficult it was to tell who might be a Death Eater - of how the Death Eaters seemed to be potentially all around, difficult to know who to trust...
Item: Crouch was broadly popular during the war years for his hard line against DEs and "Dark wizards" of their ilk, but after the war gradually lost public support for continuing this hard line past what the public thought appropriate, and he was reportedly desperate to 'catch one more Dark wizard' even in Harry's day.
Item: in all official non-Voldemort-controlled Ministry references for the public, Voldemort is referred to by circumlocution; it seems to be only Dumbledore's, not Ministry, policy to refer to him by name.
Item: the Ministry, unlike any nongovernmental organization we see, we know to have both the capacity and willingness to maintain and deploy, for purposes of law enforcement, forms of direct magical tracking of the wizarding population. Including, of course, related to the upholding of the all-important Statute of Secrecy.
Item: the only time we see Voldemort or his henchlings do something direct and purposeful to make his name unmentionable is in DH, after the DEs have gained control of the Ministry and are using ITS resources to track the tabooed name. In order to identify, locate, and capture his opponents, who at this point he has long known will deliberately use his name as a point of pride and illustration of their defiance of his threat. And it works quite well for that purpose, no?
What might we make of these facts?
Perhaps that Crouch's policy change on Unforgiveables wasn't the only action the Ministry took in response to the Death Eater threat to Secrecy?
Was it the MINISTRY - Crouch's DMLE - that made the name 'Voldemort' unmentionable to the wizarding public, not Voldemort himself directly? In response to the rising panic at the DE threat, tabooing the most specific name his followers seemed then to know him by as far as the Ministry could tell, and just possibly specific phrases relating to the mention of directly ending Secrecy as well, in order to identify, track, locate, and take down Death Eaters and their fellow travelers? Without word of their arrest or detention for questioning allowing other DEs sufficient advance notice to flee before they are forcibly revealed by their compatriots, like Karkaroff holding out (he thought) on turning in Snape...
While, unfortunately, perhaps sweeping up a few accidental wrongly-suspected people who had had the misfortune to say one of the tabooed terms. Leading to outrage on behalf of those known to have been wrongly targetted, suspicion regarding those who had seemed not to be supporters but been unable to clear themselves (or their relatives to posthumously clear their names) beyond any doubt, and general fear in the superstitious wizarding public of saying anything specific that might get one swept up by the Ministry or mark one as a fellow traveler. You-Know-Who. He-Who-Must-Not-Be-Named. Ending Secrecy. The unmentionable but overwhelmingly terrifying, ever-present threat that everyone knows about and that nobody even really wants to think about, much less name specifically. As if merely speaking of it too concretely might make it happen...
And the DEs, after noticing a pattern, would naturally switch to using terms and a title for their lord that are so general and widespread in wizarding society as to be pointless to taboo. No pressing need to spell out their own goals to each other...
As would the more superstitious and/or Ministry-vulnerable members of Dumbledore's extra-legal, anti-Voldemort but muggle-linked semi-secret Order: speaking in vague terms on issues that THEY might, conceivably, not want the Ministry poking them too hard on even mistakenly, but using that term that they specifically can say they are not using as an indication of support for anything illegal. If even they dare. The name of their and their leader's declared enemy. Pointedly as an illustration of their bravery and declaration of their cause - or at least, so understood today: if they get swept up by the Ministry, they can truthfully claim to be anti-Voldemort, but during that initial period of the policy's implementation they would have been at risk themselves. Insofar as Dumbledore's Ministry spies couldn't make sure to intervene in time to either clear the person or get them questioned instead of killed. A risk only Dumbledore himself, Harry Potter, and a few of the other longtime committed Order members and their families really seem to take care to pointedly defy by saying the name, in general.
At risk until they could be sure the taboos were lifted. If they ever were. If they even CAN be.
Which, even if so, might not have been entirely clear to them or the wizarding public ever. No point letting your suspects know you've stopped tracking them, after all.
If Crouch did authorize a policy of strategic taboos along with his Unforgiveables policy, and then either refused to lift it after the threat seemed past, or done so only very quietly and reluctantly, or been UNABLE to lift them, this might explain the superstitious use of circumlocutions to Harry's day. As well as Crouch's pressing need to catch one more Dark wizard: not only to make himself seem relevant again, but to justify his continuing or irreversible use of taboos that had referred to a now-suddenly-exiled threat and that swept up more potentially-innocent people in their net, once most of the provable DEs were dealt with.
Taboos that were either strategically reimplemented, or simply seized on for a new purpose, by Voldemort's forces once they took control of the Ministry and its tracking apparatus.
And consider: if Ministry-employee Arthur Weasley had ever even once mentioned to, or just in the hearing of, his chess-tactician son Ron the fact that the Ministry could, had, or still was tracking tabooed terms like Voldemort's name among non-Order people, might not that memory, lingering in his subconscious, years later have prompted an uneasy sense that mentioning Voldemort's name, as a Voldemort opponent on a secret quest, during a Death Eater reign at the Ministry, could be a bad idea? Even if, at that moment, he couldn't quite place exactly WHY?