I think, in spite of other's comments about it not being the "best written" or "classic literature" that is one of the amazing things about the whole series.
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.
Even things that are seemingly “throw away” scenes come back. Sirius’ flying motorbike is the most obvious. Fred and George play the, “I’m not Fred! He is!” gag on Moody that they played on Molly at King’s Cross in SS.