> However: those European acts that were called "Techno" in the early 80s are now retroactively called "Electro" or "Synth Pop".

This has been my core insight, any one person you are talking to may well be correct given their location and time that they learned about these things.

To 2023 me, "Electro" doesn't have enough information to know for sure what music you mean, but in early 2000's in the Australian club scene, Electro was a specific sub-genere of modern club house. We would probably call it electro-house now that it's not the current zeitgeist.

The fact that I know for sure people will disagree with that is how I know the former insight is right, it's very dependent on time and place, and there is no authority.