I always thought it was like in the 5 doctors where they all walked into the same Tardis but wound up in the Tardis they wanted to be in, or something like that, it's been a while.
I fell asleep listening last night listening to the Wrong Doctors but they seemed to tie Mel's actual origin into the trial of a time Lord and dinosaurs.... However Colin and Bonnie should know, unless I'm remembering things wrong that the whole Evelyn era happened between Melanie's tenure while she was working as a handmaiden for Davros...
Did the writers get confused or did I?
(Or it's possible if I actually listen to the whole thing this discontinuity will be resolved.)