On # 12, there were NO bunkers behind the green in 1935[/size][/color]
Whitten says you are wrong, and that in 1934 there was a small bunker on the hill behind/above the green.
Wexler says in his GCA essay on ANGC that you are right, and that Mackenzie wrote about that. But I just looked at the sketch Mac made, in 1931, of ANGC, that Wexler reproduces at the start of his essay. While it's hard to tell exactly, it looks like Mackenzie drew a small bunker behind #12 (then #3) green.
Wexler also says Mackenzie planned no bunkers around #13 green:
"Like the twelfth, MacKenzie’s plan for the thirteenth green indicated a complete absence of sand, but again, things seem to have evolved quickly, as three flashy bunkers were carved into the back hillside either during construction or in preparation for the inaugural Masters."
ETA: fwiw, the new Tiger Woods Augusta game also shows a bunker behind #12 green. Of course if Tiger's game is based on Whitten's article, that might not be surprising.