By "show name", did you mean "title"? We should at least have gotten that one.
What other tags should we have retrieved?
Yes, title is correct.
As far as other tags, there are at least several others that would be useful. Here are the tags I would grab and what tag I would populate in Media Center:
WTV Tag -> Media Center Tag
Title -> Series
Subtitle (this appears to also be tagged as "episode name") -> Name
Program description -> Description
TV credits -> Actors
Directors -> Director
Producers -> Producer
Broadcast Date -> Date
The TV credits content looks like this:
Mariska Hargitay/Ice-T/Kelli Giddish/Danny Pino/Raúl Esparza/Peter Scanavino;;;Harry Hamlin/Dreama Walker/Peter Gallagher/Delaney Williams/Jenna Stern/Myk Watford
So it's delimited by slashes and semi-colons. Everything up to the first semicolon is the list of main actors and the other names are secondary credits (guest stars). This specific example is from the most recent episode of Law & Order: Special Victims Unit that aired on 1/7/2015 (S16E10). I don't know if the number of semicolons is significant.
The Directors and Producers fields are definitely not always populated and probably aren't worth bothering with unless it's easy to include them.
Broadcast date is the original air date. In the absence of series and episode numbers, this might be an alternative way to get the rest of the info from tvdb and would at least give the user useful info to work with in figuring out the series and episode numbers.
I hope this is helpful.