You can get the runtime for an AppImage with the --appimage-version command line option according to AppImageKit#command-line-arguments.
With the Krita AppImage, I got:
$ ./krita-5.2.14-x86_64.AppImage --appimage-version
AppImage runtime version: https://github.com/AppImage/type2-runtime/commit/2df896e
I don’t know where to find old AppImages to check.
(Thanks for the idea. I’ve updated the wiki & post with the instructions).