why only debunk it the day or two before though ? the 15th has been touted for a long time ?
You don't debunk everything that is made up, however fanboy hysteria has been raising exponentially coming up to a completely made up release date, hence there is more reason to comment on it now.
Lets say two weeks ago, 15th Oct was one of about 15k different guesses on various forums. The 15th is the random internet rumour made up by 52 separate people that gained traction, so now they are commenting on it.
This happens, errr, with every single release, though much more with AMD. Largely because they keep secrets a hell of a lot better than Nvidia, and well, some you get the general feeling is mud being thrown around by certain people to try and make AMD look bad.
For MOST releases of MOST hardware there are multiple NDA dates where various different bits of info get given up, because there are dates that some people have to know final clocks, there are dates the hardware needs to be sent out, there are dates reviewers need the cards by, dates for media press days with limited info that have to usually be done relatively far in advance on a suitable day. IE if you have a release in say November, mid September might be the best travel/non holiday conditions when you factor in world press attending an event.
The 15th might well be AN NDA lift, it doesn't make it THE nda that we should care about just like AMD put on a media press day, that didn't mean it was the media press day most end users actually wanted to hear.