Bear in mind that the following is from my memory of reading these forums late one night... and it is second hand:
I basically heard that all of the books are pretty much the same (except for maybe errata being corrected), except for Ochem. The 2013 Ochem books actually took some material out and shortened them. I don't know if it was partially replaced by other information (e.g. There is no nitrous acid with amine reaction in the 2012 edition, but it is on the AAMC list of topics).
Basically, the old editions should still be fine, just use AAMC's list of topics to guide you.
Edit: In regards to the Nitrous acid with amine reaction,
it can be found here. Also, the reaction forms a diazonium salt, which IS covered in the 2012 edition.