Of course moving pax around was more of an issue on the tail engine jets when it was quite common if the aircraft was lightly loaded to have it filled up from the front.
There is also the all people are not the same factor which kicked in ona flight i took from LHR to Frankfurt on a long LH321. I and my two colleagues were in the very last row and a cc comes back and asks if the three people in front us can move forward for weight and balance reasons
All east Asian and around 5 ft in height they count have weighed much. the three of us on the other hand still in the back row would make a decent rugby front row with a combined weight of about 50 stone ( about 320Kg) so I doubt moving the girls made any material difference to the Cof G at all.
Also flew on a BAe146 along with the Toulouse rugby team/squad , bit of a difference in weight between them and the standard pax weight, some of them were literally gigantic - assuming the gate staff knew who was on the plane would they try and seat the big guys as close to Cof G as possible?
There is an old story of a flight leaving -in fact nearly not leaving - somewhere because of Cof G issues as it had a lot of people up front who were valuable coin collectors and effectively had carry on s full of gold.