DVD timeline mystery

[hp_lexicon]

No: HPFGUIDX 55601

Last night I spent some time updating the Lexicon's day-to-day 
calendars of the first two books, integrating the DVD timeline a 
little more closely with what was already there. I discovered 
something very interesting. 

They have a date wrong. 

No, wait a sec, hear me out. They have a date wrong that they 
shouldn't have gotten wrong, because it's a no-brainer. They put the 
date of the visit to Hagrid's for tea as September 7. That's not 
possible. That's a Saturday, and the tea was clearly stated as being 
on a Friday, the afternoon of the first Friday of their first week.

So what, you say? There are plenty of date issues we could bring up. 
What's the big deal?

The big deal--and this is kind of weird--is that *I* had the date 
wrong on my calendar. Without realizing it, two years ago when I was 
creating that calendar, I plugged that event into the Saturday slot 
instead of Friday. I never noticed it until I was going over things 
last night. I had it wrong. 

Now I suppose there's no reason why they couldn't have made the 
exact same error. But I can't help but wonder how it happened that 
they reproduced in their timeline the same error that was found in 
mine. 

Curious...

Steve Vander Ark
The Harry Potter Lexicon