Delete Post- Wrote something then decided to remove however they don't let you remove so I just edited to say Delete.

The seating capacity would not come into play for the 737 due to the payload and basically all 737 not operated under 91k, 121 or 135 that are carrying passengers will operate under 125. I believe most try to operate with less than 20 so that they are not required to have a flight attendant on board per reg but I could be wrong about that. The only reason I brought 125 up was because they have there own training and testing requirements in addition to which would have applied to your first example.

Using your GV example then...Assuming that you are current and typed in the aircraft (3 landings etc...) I would argue that you would only need to become familiar with the aircraft to the extent the differences apply per 61.55b1. However if you wanted to know what those differences were then on the GV product I would recommend familiarizing yourself with the guidance that a 135 or 142 training center would use and comply with: (Flight Standardization Board Report Rev 8.GULFSTREAM GIV-X (G350/G450)
GULFSTREAM G-V
GULFSTREAM GV-SP (G500/G550)) In the case of GV it is all A,B,C lvl differences and does not require time in the variant aircraft.