Dec 2011 to Jan 2012 – Bargain for Used Car?

I've kind of zeroed down on a used car (2009 Accord EX-L) however looking for pointers to negotiate.

Say if KBB value is $19500 for Dec 2011 what possibly it will be in Jan 2012 – From a book perspective the car is older by an year.

No, it's not older by a year you idiot. It's older by a day from 12/31/2011 to 1/1/2012. It makes no difference what-so-ever.