I do not know this for sure, buy I suspect that all "stale" stock is shipped back to Apple and they are sold through other dealer networks (amazon, macmall, etc.). I seem to recall a post a couple years back about this...
For those in the UK - I was at the Apple Store Regent St last night and asked about the 17" MBP.
New one wasn't yet available but the previous model is now £1,749 - which is only a £50 saving, given that the price has dropped by £100 anyway. I can't imagine anybody wanting to buy the "old" machine at that price now though so I suspect they may have to adjust this.
Didn't bother asking about the 15". They did already have the new 15" in store.