Okay, the old ones that apparently have both do have the Thunderbolt symbol on the ones that are, though, so what’s the problem?

The only devices that don’t have at least Thunderbolt 3 on all ports do use the Thunderbolt logo on the ones that support it, except the short-lived 12-inch MacBook (non-Pro, non-Air). Basically, for data transfer:

• If it’s a 12-inch MacBook, the single USB-C port doesn’t support Thunderbolt, and only supports USB 3.1 Gen 1.
• In all other devices, if the ports are unmarked, they all support Thunderbolt 3 or higher
• If the ports are marked with Thunderbolt symbols, those ports support Thunderbolt but the unmarked ports on the same computer don’t.

For power delivery, every USB-C port in every Apple laptop supports at least first generation USB-PD.

For display, every USB-C port in every Apple laptop (and maybe even the desktops) supports DisplayPort alt mode.

It’s annoying but not actually that hard to remember in the wild.