I'm going to use this post to work out some thoughts I had last night while watching The Chamber Of Secrets. You are welcome to read and comment on them, and I rather hope you will.
The whole thing started with Tom Riddle's declaration of being a 16 year old memory preserved in a diary for 50 years. For some reason, this made me think about various ages and dates which I scribbled on the back of a convenient envelope. It was midnight, so be thankful they even make some sort of vague sense. I'm going to try and recreate my thought process here so bear with me.
So we know that CoS is set in Harry's second year at Hogwarts, he's 12 which makes the year 1992. Tom Riddle is a 16 year old memory from 50 years previously when the Chamber was first opened, so that would be in 1942. The original thought I had was that in 1992, Voldemort would then be 66. I'm not sure why, but that seemed to be an important fact at the time.
Anyway, this then led to another thought. Why did Voldemort create the diary in the first place? I checked the book and found that Tom says that "one day, with luck, I would be able to lead another in my footsteps, and finish Salazar Slytherin's noble work." (CoS page 230) Now I took this to mean that it would be the memory doing this. So could that mean Voldemort knew in 1942 that he wouldn't be able to do it himself and would have to rely on his 16 year old self to do so?
HOW??
The Prophecy is dated to 1979. Dumbledore tells Harry it was just shortly before his birth (OotP page 740) and the label on the shelf in the Ministry is dated some sixteen years previously (OotP page 688). Does Voldemort have some other knowledge from a source he gained before Trelawny's Prophecy? What does he know, and where did he get it from?
Does this explain how he knew that it was Harry that the Prophecy referred to rather than Neville?
Another thought. Ginny got the diary from Lucius in Florish & Blotts. Was it a coincedence that she got it or was she specially chosen? If she was specially chosen, why her? I presume that Voldemort told Lucuis at some point in the past to give the diary to Ginny, but was he also told that Ginny would be in Florish & Blotts at that time?
A couple of possibly important notes and questions to finish off with:
Tom knew he was the Heir of Slytherin. How?
The Heir of Slytherin is Muggle-born, which pretty much goes against everything Slytherin stood for, and also Voldemort as well. Was this done on purpose? How did Slytherin's Heir end up being Muggle-born anyway?
Why didn't the Heir know where the Chamber was? Tom says "I wasn't going to waste those long years I'd spent searching for it." I find this slightly odd. He knows the Chamber exists and what it's there for, yet he doesn't know where it is??
If Tom had suceeded in eradicating all Muggle-borns the first time round and refusing entry to Hogwarts, what effect would that have had on the wizards and witches who are around now? Obviously Hermione wouldn't attend Hogwarts, but what about Harry? His mother would be denied attendance, but is Harry classed as Muggle-born or pureblood? Also, Voldemort's intention would seem to be to get rid of Muggles full stop so there's every chance Harry wouldn't even exist. Is this linked to the fact that Voldemort knows Harry will kill him in the end?
If Harry hadn't managed to stop Riddle in the Chamber and he did actually return, would there then have been two Voldemorts - the one from 1942 and the one hiding somewhere after Harry's attempt on him at the end of his first year? Surely that would lead to no end of problems and paradoxes.
Now in 1942, the Headmaster was Armando Dippet and Dumbledore was the Transfigurations teacher. Hagrid wasn't the gamekeeper till after his expulsion, though I'm sure I remember reading somewhere - I think it was in
The Harry Potter Lexicon, that Mrs Weasley remembers a different gamekeeper. The suggestion there was that there's something funny happening with time. I'm not so sure I agree with that, but there certainly appears to be something going on. Has Voldemort been messing around with time and that's how he has this knowledge? It's a most intriguing thought.
NB:All quotes, page references, etc are taken from the hardback copies of the UK editions and are copyright JK Rowling, Bloomsbury and Warner Bros as applicable.
My head aches now.