Are you kidding? When have they not? Apple II, II+, IIc, IIc Plus, IIe (also //e), IIe enhanced, IIGS. All sold concurrently.

They’ve always been this way.

Bad example, but very true with the Mac under sculley. When Jobs came back that was one of the things he greatly simplified

Most of those models were not sold concurrently. The Apple II, II+, and IIe each replaced the previous model; the same was true of the IIc and IIc Plus. "//e" was an alternate textual rendering of IIe, not a separate model.

The most Apple II models that were sold concurrently were the IIe Platinum, IIc Plus, and IIgs. (And this was around 1990, at which point there were far more models of Macintosh computers on the market.)