[Corin Stormhands]

Okay, so help me out here.

I forget which of the last books had the letter from Dumbledore(?) reminding Petunia of his last letter. Somewhere upthread someone mentioned that might have been the letter that came with Harry, but I’m not so sure.

Was that just thrown in there to throw us off? I don’t think Snape’s memory answered that question.

[null and void]

I forget which of the last books had the letter from Dumbledore(?) reminding Petunia of his last letter.

OotP, after the Dementor attack, when the Dursleys are preparing to throw Harry out.

Somewhere upthread someone mentioned that might have been the letter that came with Harry, but I’m not so sure.

I can't think of any particular reason why Dumbledor would have needed to correspond with them after that.

I don’t think Snape’s memory answered that question.

No particular reason Snape would ever even know of the letter.

[Maigrey]

IIRC, it was book five, when Harry was about to be thrown out of the Dursley house, and a letter came to the house, addressed to Petunia, saying, remember my last.

His last could have either been the letter he left with Harry when Harry was dropped off at their house 15 years prior, or when Dumbledore replied to Petunia years ago, when she was trying to get into Hogwarts, that she could not do magic, but be use in the muggle world.

Personally, I think it was the letter that Dumbledore left with Harry when he was dropped off 15 years prior.