To write about a maximum, one has to have encountered said maximum Until recently I did not know that money building max level or skill max level even existed.
But these are stats that start over after a reset. Girls stamina does not. If there is a maximum, it is higher than 80 per position and I cant rule out a maximum total stamina.
From a mathematical viewpoint, they do not need to implement a maximum. If it takes you a week of constant filming in the best studio to increase a girls stamina by 1, that is a practical maximum. Would anyone know the growth of the positions? From one level to the next. It is hard to read on my display.
And with the numbers, I presume they will switch to 1k if you near 999. Like everywhere else in the game, including the exp in the filming scenes.