UPDATE:
I chatted with a rep from Trek and she/he (name was Lo) walked me through quite a bit of parts interchangeability. Said, as others here have, that just the application is enough to find a suitable replacement. i.e. For the front derailleur just the function will work - Front Derailleur 3 Speed - is enough to find a replacement.
I'm learning......
I also watched a video on YT by Seth from Berm Peak which cleared up a lot mere.