Add another condition to your simulations. For both Simulation A and B, buy new girl as soon as you have the gold. For A, have the newly bought girls start working. For B, train them and then set them to work.
If you run it under the conditions of the first set, the income gap gets larger in favor of trained girls. In the second set, the income gap gets larger in favor of untrained girls.
How are you doing the simulation by the way?
I created the 5 girls with the appropriate stats for each set of tests, then I chuck all my other girl packs and start a new game. On turn 1, I set up the brothel (buy strip bar, hire staff/gang/matron, auto buy potions, etc.), save the game and quit. Rename the save files to "Test.gam" and "Test.gam.mast" (enables cheat mode - which does many things, the only relevant one being that you can take an unlimited number of walks in the city each turn and each one gets you a free girl). Take 5 walks to get 5 girls, save the game, and quit. Load save under the brothel name (the game always saves under the brothel name, so the "Test" files don't get overwritten here - all cheats are now disabled), set house percentage to 95% for all girls, and assign girls to their appropriate duties (run A gets brothel duty, run B gets training duty). Let time pass, interfering when the matron screws up, the guard gang gets the shit kicked out of it, etc. Save frequently so you can go back in time if one of the girls dies on you. In run B, frequently check on the status of the girls training; it takes about 8 months for a girl with 0's across the board to get to max out all skills and stats (training time doesn't vary between sets). The 5th girl in the training runs will max out after the other girls. Put girls on brothel duty when they max out.