Well if she pass from agency to indy, its easy to keep contact and keep booking her, unless she is terrible at her schedule working.
If she switch agency, it depend on where she go. I guess for a girl you really like, you will call another agency to see her again, but of course it really depend on the kind of service you get. If i would like a girl a lot and she pass from a great agency thats always on time and such to an agency that is 45 mins late, or cancel often, then i dunno if i would try my luck many times...
But when it comes to new girls , its easier to book them with your fav agency when you know you will get top booking services. To me thats really important. If it start "sur les chapeau de roue" et j'ai du attendre 45m, ou jme suis fait bullshiter ou whatever... meme si la fille est sa coche... je garde un ptit arrriere gout de l'experience de booking. Alors que quand je call/text, tout se regle super vite, la fille arrive dans les 10 mins... Alors la wow sa pars bien.
But again i already said it before, parties parties parties... sometimes its crazy how a person vibe make such a difference. You want to meet her badly because of that feeling she gave you. Other time it can be the other way around, a complete turn off when you expected her to be totally your type. But im going a bit off topic...
So following a favorite girl? Yes, but on certain conditions. Booking services to me are really important to my experience.