That raises a completely different question: the Glasgow Queen Street stop north/west bound, is pick up only. But yes, it can and does happen.I was on one night running late and we had some passengers alighting at Glasgow. Not sure how, but the crew were aware of them being onboard, so they clearly had it officially agreed.
As we passed Edinburgh Park the TM came down to tell them we were diverting so they'd have to come to Dalmuir.
So yes, it can happen.
What, if any, arrangements are made for affected pick up passengers is a good question.
Stops after GLQ would seem to be the risk averse option! 


