It doesn't give the year though, Harry was born twenty six years before Storm Front, but it doesn't give the year that Storm Front takes place in.
It gives at least a couple of years and the reasons for and against them.
I'm not sure if I've ever heard of a five year old wearing diapers who didn't have severe issues, but my mom doesn't think it would be that unusual. (My mom has more experience with young kids below the age of 6 or 7 than anyone I've ever met including kindergarten teachers and pediatricians).
Not exactly a continuity error, but Harry attributes the Hounds of Tindalos to H.P. Lovecraft. They were created by Frank Belnap Long and later incorporated into the Lovecraft Mythos by August Derleth.
Yeah. (1)Harry mentioning the Notre Dame fire, (2)Lara saying she changed Thomas's diapers after he was five, (3)Murphy's P-90, and (4)the Hounds misattribution can all be easily explained. 1. Harry "wrote" this or all the case files well after the fact. 2. Either Thomas or Lara was wrong about the timeline. 3. Murphy got a second one, or depending on when it reappeared, maybe it washed up on Demonreach after Harry had claimed it. 4. Harry (or Jim) was just conflating Lovecraftian with Lovecraft.
Those are all things that people do, so it wouldn't be nonsensical if it was just that kind of mistake in text. The whole "it's all written by Harry years after the fact" theory can make a lot of the continuity errors go down smoother.