I actually have a counter-example in LHR.

The IAD-LHR printing me the JL BP above? That was actually a long layover (I got into LHR T5 at 7am and my JL44 flight was almost 6pm) so I went landside to mail some shopping and crossed over to T3 landside (HEX I think).

I approached the JAL desk which was checking in the earlier JL42 flight. The JAL T3 check in desks were crewed by three contract agents plus one uniformed JAL supervisor. I explained to the supervisor I'd like to confirm docs check is complete, my Visit Japan Web is ticked off (BA IAD totally missed this) and my BP to be reprinted by JAL to evidence everything complete just in case I cut things too fine in the afternoon and have to make a gate dash. Supervisor understood and directed me to one of the contractor desks.

Contractor was flummoxed that an afternoon JL44 customer is trying to check in now and refused my requests, she seem to think the morning desk cannot check in PM flights. I waved for the supervisor to come over and the supervisor authorised the check in for the next flight.