When I was younger I used to remember far more about all the details of a picture, but as I get older, I remember less. Partly, no doubt, it's old age, but also, I think, it's having taken tens of thousands more pictures and realizing that the picture is the thing. Of course, for 20 years or more I've had all kinds of review cameras and lenses, but even 30-35 years ago I had screw and bayonet Leicas, Nikon Fs, Nikkormats and a Pentax SV in 35mm alone. If you have only one camera, or only one or two lenses, it's a lot easier to remember!
Quite often I can remember the camera or lens or both with absolute clarity, but what prompted this thread was a few B+Ws from the 70s where I genuinely don't recall what camera I used, or even what system: I was just in one of the places I took pictures often, and in some cases it probably depended on what had film in it that day. From the 90s on (I was 40 in 1990), I cared less and less.
Cheers,
R.