Thanks for the clarification. I did not know specifically about the two extra Revvivo Bs ordered to go with the RBDe 566.
When I first rode the VAE (1998). There was one consist which had a SOB BRD and one EWIVA and three EWIVB. There were 2 other consists, one with SOB BRD, one BT EWIVA and 3 EWIVB, one with BT BRD, EWIVA and EWIVB and AFAIR one that had SBB EWIV coaches and a BT BRD. I think that one consist was held as reserve each day while the remaining sets were in bi-hourly operation.
As far as I remember, two of the original BD had been converted to pilot coaches by the BT (I don't remember the date) and two had been sold to the SOB in the 1980s and had been running as BDt pilot coaches since then. The BT pilot coaches were running with either the so-called married pair coaches or with regular BT EWI stock. Other BT consists were running using one of the ABt from the original BDe EAV acquisitions and the other was running on the renovated ABt 141 rebuilt out of an older pilot coach.
I have seen photos of the models (and my Wabu coaches) have different UIC numbers. Can you clarify when the coaches would have had which markings 50 47, 50 48. I seem to recall some rolling stock also had 50 62.
This is information that I remember seeing on a website, but that website, like a lot of others from 1998-2010 is no longer actively hosted.