Hmmm...I haven't done immediate test-retest of my adjustments, but when I went through the AFMA on my 5DII, I also retested 4 lenses (or so I was thinking at the time) that I had previously AFMA'd on my 7D, with 4-6 months between tests. Two of the four (85L, 100L Macro) were the same, one was different by one unit (70-200mm II went from +1 to +2). The fourth lens was the 24-105mm, and that one had a substantial change - then I smacked my head as I realized that it wasn't the same specific lens - I initially bought a used copy, which I sold when I bought the 5DII to get a new lens at the kit price. So, of three lenses retested two had no difference and one changed by one unit.