Evidently opinions differ on this, however personally I feel it’s a little presumptuous to be making a point of asking a fellow member of staff to display all their documentation. I get that there’s a chance something might not be in order, however personally I’d be inclined to have bigger fish to fry in the grand scheme of things.
From what I understand the encounter I referred to was on the Stranraer line so not exactly the heart of the empire, but to me it seems to contrast sharply with what one normally gets which is that the slightest hint of a PRIV or any kind of staff pass and the guard will be straight onwards.
For priv passes, they do indeed get a cursory brief inspection and a wave of the hand and I move on.
For priv tickets I always show mine with my pass and I don't understand why anyone would be so arrogant as to a) not do so in the first place and b) to take offence at being asked for it, the same as any other discount pass and ticket.
They offer a significant discount and can be and are misused - not all railway employees are honest (see the GWR deputy director who has just been done for mass fraud).
As for rather not know - I value my facilities and I have no time for misuse of them in terms of lending them to 3rd parties or whatever. The most recent time I've known a priv be withdrawn by someone at our depot (it's fairly unusual and big news when it happens) was a Male retired staff member giving a female friend his boxes to go on holiday with. That is taking the mick.
I have always been trained by old school people and work very much in that vein and the first rule is respect your colleagues and particularly with regards to putting people in positions of responsibility in uncomfortable situations by your own omission.