Christie is listed with www.ny_escorts.com
Giselle is listed with Mona Lisa Models.

Both sites have the same photographs of the same provider and similar bios.

Did not see any other Mona Lisa Models.

So what conclussions can be drawn from this?

Not uncommon for escort to work through multiple agencies. I can cite a number of recent cases. Escorts increase their number of appointments plus they can give priority to agency who charges higher fee. I use monalisa alot and they'll tell me who is exclusively with them; they're very honest. The exclusives I have found give better "service" because they are totally dependant on one agency to fill their appointments, good clients like me will give feedback to agency, they are not as busy thus unrushed, and they will have reviews under only one name.