Great Balls,
I have no idea what that survey form was and will ask my manager if Mixed Fleet are handing out surveys on only their flights but it is definitely not normal.
It saves BA a fortune not having them on board now and the results are more scientific because it is totally random instead of using seat numbers etc.
I have seen a lot of Mixed Fleet flights going out with two senior crew on and it will probably be because some of them are new and are being given a supernumerary flight to show them the ropes or it could have been a Mixed Fleet manager doing a check flight because they wear exactly the same uniform as the CSMs. Maybe that's what the survey was about, don't know I am afraid.
I just realised that the second crew member may not have been a CSM. If it is a 319 you only get three crew unless the Club cabin has more than 20 passengers, then you get a forth. If it is a 320 you get four crew always but if the club load goes over 40 you get a fith on that Bud route. That is probably why you had one at the front one way and two the other.
These are my own views