The National Rail website page doesn't show that restriction. Is it new, or has it been missed off the page? (which does seem rather spartan, so wouldn't be surprising).
Yes, there's a whole section titled "Details" that's present in the others but missing here. Presumably this is a failing of
GWR▸ 's (I guess) information management within whatever mysterious and complicated process puts these pages together. Rovers & Rangers are now shown in
BR▸ Fares, which is an easier place to find the information, and evidently more reliable.
I see that the fares on the National Rail website haven't been updated either.
On split ticketing at Tiverton Parkway, and the point about the train not having to stop at that station. What happens with, for example, the train that leaves Taunton at 08.57 and arrives at Exeter St Davids at 09.23. It doesn't stop at Tiverton Parkway, but would obviously be passing through after 09.00, but would it be counted as a valid service to use?