If they don't know the rules, they shouldn't be defensive or try to deny travel due to their misunderstanding. Take the approach of orange = good and let the customer through. An issue is also the infrequency that any of the more complex National Rail rules come up, the number of people using paper tickets to travel within the London Zones and take advantage of break of journey rules (for example) is a minority of this forum, and probably unheard of elsewhere.In their defence, the TfL issues are really only at stations where there is a National Rail to TfL interface. I have sympathy with them: they have to learn all the TfL rules and then have to learn- and recognise- when National Rail rules are different.
There is also the issue on TfL where it is a National Rail service but TfL deny it (Overground and Elizabeth Line).