I think truthfully, when we say a pup was housetrained by 9 weeks, it really means that WE were housetrained FOR the pup at 9 weeks. There's no way a pup, at nine weeks, etc., absolutely knows not to pee anywhere but the designated area. Granted, you may not be getting accidents, but more likely, it's b/c the human is doing a wonderful job at management, supervision and anticipating the needs of the pup to get him to the appropriate elimination area at the right times(s).
My experience has been that, for most dogs, by 6-7 months (and with proper training) they know to hold it until given access to an appropriate spot to pee and I would consider them fully housetrained. BTW, I don't consider a dog FULLY housetrained until we get three full months w/o ANY accidents.
As a puppy, Quiz peed in my house ONE TIME... but I certainly don't think he was housetrained by 8 weeks. I think I was just really good at setting him up for success and getting him out at the right times to teach him the correct place to go.
(Golden Retriever) Born 5/12/12, Adopted April 2014.
Wordsmith's Winsome Warrior
No titles (I'm too lazy now!), but an awesome hiking partner! "Quiz"
(Golden Retriever) 12/31/03 - 3/20/13
U-CD Tanbark's Number Two Pencil, JH, CDX, Can-CD, AX, AXJ, OF, RS-E, JS-E, GS-E, WCDex. I loved being this dog's partner! Watch him shine! "Zoie"
(Whippet) 9/8/00 - 3/28/14
Donmar-Valair Second Wind, CD, RE, MC, ASCA-CD, Th.D.
#1 AKC Obedience Whippet for 2004 / AKC and ASFA FCH Pointed