I wasn't really thinking about that one, that stock wasn't compliant for accessibility although there may have been more / other reasons as to why the MKIIIs were not used. I'm thinking more if/when the 397s are replaced on odd services due to issues with the booked unit. Most passengers would likely just shrug it off as one of those things, but there are always those that might kick off.
Say a 185 replaces a 397 on a particular service. Firstly the disabled passengers would have to be accommodated in the usual place in the vestibule next to the First Class section, and not in it. This in itself might be perceived as an issue by a few, and not one that could be resolved because there is no suitable area for them in the First Class compartment. Then the passenger may not be offered the usual First Class service because a) They are not in First Class, and b) a 185 replacing a 397 might be so busy that the passenger would be surrounded by standees.
Hopefully it would be a very irregular occurrence, and as I say most would just get on with it. I'm just thinking aloud really, wondering what might be the policy in such circumstances.