Previous Alphas.
Not having played games in a very long while, and starting out with no RTS experience - whatever - playing A23 on a raspberry 4. I loved it, though I hadn't realized how slow the play was at first. I then installed Mate, which has a25 in the repos, and suddenly I was better. At first, until the ai was preparing an large scale attack. I played in a25 for almost a year, before forcing an upgrade to a26, liking it and moving to MX Linux which is faster and installs a26 by default.
I hadn't noticed any building changes between 23 and 25, so looking for that had not occurred, but next time I'll look more closely at change lists and videos.