I find this is an interesting topic and have always wondered about it.
I ran some AAS in the 90's (Sust., EQ, small amount of Dbol - no A.I. back then) and then didn't touch anything until this past year for a cut / recomp. since my body fat was getting too high and I believed my Test. was running low.
Before I started AAS, after a few months of consistent training, I made it to 250 (still higher BF) and matched or passed all of my previous numbers on all of my lifts. The muscles may have not been quite as full but it seemed that muscle memory was real to me.
OD
Well there must be something to muscle memory if how you look in your avatar is only after a year back on training.