Do we have to go down this path again?!?
I am actually confused by what you are saying here. You asked them to produce the policy (I don't think we need to get into the formal definition of policy - lets call it Disney Standard Operating Procedure) that says you CAN'T use a Fastpass after the return time? Was this when you got turned away somewhere?
The DSOP, as most clearly defined as us non-CMs can get and as told to us by CMs, is that late Fastpasses, issued the same day, are to be accepted,
unless the attraction manager on duty says otherwise. Why they would do that is a completely separate debate, and we don't need to know the reason - it is up to the manager. Now they supposedly have guidelines with regards to this, and if it happens it is rare - and typically only at Soarin', and perhaps TSM. Mechanical issues is NOT one of those reasons, because the CMs will in fact announce that the Fastpasses ARE valid any time that day in those cases - not because of the issue, but because it is the DSOP.
CMs are supposed to be trained to understand that late FPs are ok - but we also know that some CMs understand that or remember it better than others, as well.
Now, as in an earlier case - if it is evening EMH, and they are not issuing Fastpasses during EMH, you may or may not be able to use a Fastpass from earlier in the day...because the Fastpass line itself may be closed. I have not checked on this myself - I'm usually far too tired to make it to an EMH these days...