The main acting credits order in films is an interesting question as well which I guess could maybe be answered in a similar manner. Some films order actors alphabetically. Some by appearance. And some order the first N by some contractually reasoning, but then presumably the rest will be ordered less strictly, possibly somewhat randomly. I've always wanted to tackle the problem of trying to standardize the lists somewhat.

Just an example to explain what I mean. The film Bard Wire has an alphabetical cast list (so Pamela Anderson Lee, as she went by at the time, is mid way down the credits). Interestingly the "three actors" listed by IMDb has Anderson first, but then the next two are just the top two on the credits. It would be useful, to a degree, to try and figure out who those second and third people should be based on some metric.