DISCLAIMER: I Am Not A Mod™, so the following should not be construed as official advice. However, mods have been involved in current discussions of the situation described here, and I've done my best to accurately report what's been said. All opinions expressed are entirely my own.
Now, then, what you need to know:
According to the best information so far available, the code that generates the Signup Summary does not see (and therefore doesn't tally) fandoms included in the Optional section of a "bucket list" offer. It does see all requests, and sees all offers included in the main Fandom field of an offer slot, whether that slot is used for a "bucket list" or not.
[NOTE: A bucket list is an offer slot featuring multiple fandoms in which you've offered "Any" characters; you add the extra fandoms to the Optional section.]
This is being referred to as "the bucket list bug". It is an AO3 code issue, and is not a matter over which the Yuletide mods have control. Any challenge or exchange that produces a Signup Summary will experience the same issue. It does NOT affect the actual matching process. The code that does the matching sees all and knows all; it recognizes and accounts for bucket list offers.
What this means, generally:
If a fandom is listed in the Signup Summary, its actual number of offers may be higher than that listed. Specifically, a fandom listed with 0 offers may in fact have 1 or more offers in bucket lists. OTOH, the listing may also be correct as reported.
Essentially, the result is that all those (x/0) fandoms that look unmatchable may actually have a potential match or matches lurking in the bucket lists, and many (x/1) fandoms may be more matchable than they look....but there's no way for most participants to tell for sure.
If you made a bucket list offer:
With respect to the fandoms in your own signup, you have a slight advantage in reading the Signup Summary. For example:
If you offered Ghost Soup Parallax White in your bucket list, and it's showing up as (3/0) -- that is, three requests, no offers -- in the Signup Summary, you know that there are requests out there for it and that you can be matched to at least two of them (or all three, if none of the requests is yours).
If Ghost Soup Parallax White is sitting at (1/1) in the SS and you know (a) the request was yours, and (b) you made a bucket list offer for it, you are also slightly ahead of the game. Because you know that the offer reported in the SS isn't actually yours, you know it's a potential match.
By contrast, someone who requested and offered Ghost Salad Serpentine Black -- but didn't use a bucket list -- will look at its (1/1) Signup Summary listing and think "unmatchable", not knowing that you also offered Ghost Salad Serpentine Black in your bucket list.
Should you edit your signup as we approach the last-minute stage?
That depends.
Three things you should NOT do:
• Don't simply delete a bucket list offer. The matching process needs those offers.
• Don't delete a request you want desperately, just because it looks unmatchable in the SS.
• Don't blame the mods for this problem; it's not of their making, and they can't fix it themselves.
Two things you probably should do:
If you made a bucket list offer, but still have available offer slots (remember, you have as many as 10), you should consider moving as many offers as you can out of the bucket list and into those available slots. This will make the Signup Summary more accurate.
If you have available offer slots, bucket or otherwise, do take a few minutes to cruise the long list of (x/0) and (x/1) fandoms in the Signup Summary. Invisible bucket offers notwithstanding, many of those listings are most likely accurate, and if there's a fandom among them you can offer, making that offer will (a) help the matching process, and (b) give someone a better chance of receiving a story they really, really want.
Two things you might consider as the clock ticks toward the last minute:
If all of your fandoms look unmatchable on the Signup Summary as the signup deadline nears, you might want to modify your requests (and/or offers). Remember that you have as many as 6 requests and 10 offers this year, so you may be able to add one or two without deleting existing entries.
If you have made offers for fandoms not on the Signup Summary -- that is, for entirely unrequested fandoms -- you might consider deleting those offers. This is very much a judgment call. The mods have indicated that offers for unrequested fandoms tend to slow the matching process; OTOH, it's entirely possible for a last-minute signup to include unrequested fandoms, so that the offer you thought wasn't matchable might actually "go live" just as signups end.
This has been your Muppet News Reporter, now signing off....