I know I'm late to the party, but two observations:
For Tara (re "Very very surprised to learn that Jeff Perry has a female wife"), Jeff Perry was married to Laurie Metcalf back in the day, before her marriage to Matt Roth.
2. To SnideAsides, there have been periods where three people are listed in the Doctor Who credits. Arthur Darvill was third billed for a time, for example.