I do not know for certain. I believe that 50 grafts/cm2 is pretty aggressive and damn dense and not outrageously challenging for a competent surgeon.
"Some surgeons (e.g. Shapiro) simply prefer to achieve 40-45 in 2 passes for "strategic" reasons (e.g. fine tuning at 2nd pass, assess the hairloss progression, etc.), but they wouldn't have any problems in placing 30-40 in one step."
I don't know that this is true. The best doctor for me is the one who has a lot of experience, and not the doctor "who wouldn't have any problems". Any less than 30 grafts/cm2 is a waste of the patients time; he can solicit a doctor who is able to pack nearly twice that many grafts and ultimately save the patient a lot of time and grief.
"Another reason for the 2 pass is the size of the medical staff"
I agree but such is not a good enough reason. This is why one needs to find a doctor who can provide what the patient wants, and not merely what the doctor thinks the patient can benefit from.
"Did I understand correctly?"
You made some good points.