I can think of several scenarios where you wouldnt want to use an existing stage name of a model.

1) Change in niche orientation.

Say a model is known for doing a certain type of shoot, in a certain niche and that gets changed, a change of name might broaden the appeal of that model. I beleive there are several pornstars who have more than 1 name depending on what/who they are doing.

2) Bad Press.

A name change due to recent bad press about a certain model.

3) Branding.

If a model has a specific stage name that has been branded to one company in detail, might be an idea to change the name so that every time that model is mentioned, working for your company, surfers / affiliates, dont automatically think of their old company.

Regards,

Lee