1. They choose a name and a few weeks/months later they don't like it and find a more 'clever' name to use.
2. They get surgery and choose a new name for the 'new look'.
3. Euro girls may change it for an 'American' production because they might think the original European name might be to hard to pronounce. (See Sbando Boy's eurobabe index.)
4. Some are not concerned with the name used and may use whatever the studio/producer suggests. (Think Hustler)
... and I'm sure there are dozens of other reasons.
DenverDon


