The timeline on the DVD *confirms* canon.

[mongo62aa]

No: HPFGUIDX 55894

--- In HPforGrownups at yahoogroups.com, "gwendolyngrace" 
<gwendolyngrace at y...> wrote:

So if the end of term is around June, then there'd be a roughly 
June/July cutoff, and all the kids in a given first-year will 
celebrate their 11th birthdays through the course of that year.

Gwendolyn Grace

Me:

Actually, 6th-year Cedric Diggory turned 17 sometime before placing 
his name in the Goblet of Fire, which spit it out on Oct 31.

So if Hermione does in fact turn 12 in CoS, then the cut-off date 
must lie between Sep 18 and Oct 31.

Bill