Yes, it is totally ridiculous.... Some people say it is valid unless it says other wise on the ticket... though i beg to differ, as Im sure the validity of the ticket is subject to "terms & conditions", which obviously cant fit on the ticket. Though sourcing the actual "validity" is another challenge.... but as you are adhering to their T & C's, you are still obligied to find them... though lets face it, if the conditions are so hard to find for the passengers (and even enthusiasts), Im sure your average guard will not know either, as It's pretty fair to say that many of your average guards who do it as "just a job", rather than " a passion" know less about tickets, and especially rovers than many enthusiasts....
An example to a extent is (for a barrier ticket check man) : A freind got a job on the barriers at Man Piccadilly. On the "training course" they whizzed through a few kinds of tickets, and where to find validity dates, but they never mentioned a rover. At the end he said to the training person, you've missed a type of ticket, and he produced a rover, the training person didnt know they existed!!!
Another person who I met on the Holyhead 57 on Saturday said he showed an ALR (in a ticket wallet with a YP and a YP photocard) and the guard replied "have you actually got a ticket to travel!?" and when he explained what the ALR was, he just walked on... no apology or anything... now that is poor training is it not?