I would tend to think they rented one or the other for filming and then had to re do some portions and the same car was not available?? Not too many quality replicas were available at that time.
Ferarri themselves had a close eye on the Testarossa because I believe it was a loaner, at first, to promote the new flagship Ferarri. Any "dangerous" scenes were filmed with replicas, and scenes that actually involved the the need for power or speed were filmed with believe it or not.... a Pantera with a fiberlass Testarossa body on it !
