German Rail Pass - any trains not included?

You will have no difficulty using any of the high-speed or regional trains for the routes you have chosen, including Nuremberg to Rothenburg. The fact that Rail Europe cannot sell tickets (and offers no fare) for that trip has nothing to do with whether you can use the trains.

As for RESERVATIONS, it is impossible to reserve most regional trains in Germany. It's simply not done. You get on and you find a seat. If a journey includes both high-speed and regional trains, then the only reservation you can purchase is for the high-speed train. Of course reservations on high-speed trains are not required either. I have traveled routinely over 4 decades on German Rail passes and I don't think I've ever reserved a seat. I just get on and find an empty one that isn't booked for my specific travel leg (which is indicated with electronic signage above or ON the seat.)

You are getting that message because the regional trains don't take seat reservations, which is the only thing you would be looking for through Rail Europe. For train schedules, see the Deutsche Bahn link at Looking Up Train Schedules and Routes Online. All of your trains are covered and none require seat reservations, though you could make one for the longer last leg, if you wish, about $5 in Germany or on the DB site.

Got it. Thank you both for clearing that up for me!! :)

I was only searching the routes on the Rail Europe site to look up durations & connections for the routes I have planned. I just got worried - and slightly panicky haha - when that message popped up because I thought that maybe, despite the research I had done, I bought the Rail Pass for no reason since half the routes I planned on taking weren't actually covered by it.

...BUT it sounds like I am good to go :) woop WOOP!!

Thanks again!! <3

DO NOT use Rail Europe to find train schedules in Germany. Use the website of the outfit that runs the trains, Deutsche Bahn.
www.bahn.com

You are also likely to find that you can buy the GRP directly from Deutsche Bahn for less money, rather than a middle man.
https://www.bahn.com/en/view/offers/passes/german-rail-pass.shtml?dbkanal_007=L04_S02_D002_KIN0060_PAESSE-INDEX-GERMAN-RAIL-PASS_LZ01

Roger, that - I will start using the DB site instead to look up schedules.

I have already paid for & received my GRP through Rail Europe - oh well; you live and you learn....

...HOWEVER, for anyone reading this that has not already bought a German Rail Pass but plans to, the Deutsche Bahn prices are definitely cheaper (see link in above comment from "Sam")...had I gone directly through DB, I would have saved about $80.

The trouble with looking up schedules on RailEurope is that they don't show all the connections. They only show you the schedules for connections for which they want to sell you tickets. Often it's only the most expensive trains, but then that wouldn't matter in your case, since you already have a rail pass. Sometimes I think there are just too many options to show you, but the Bahn shows you all the options. The Bahn shows you more options, but even then, sometimes faster, long distance train connections, dominate. Sometimes you have to go to "only local transport" to filter for slower, local trains to get all your options.