It seems like stranded pilots are a different category from TV Movie or TV Series. They are more like Specials. Perhaps they could be listed as TV Series with an entry at the end of the Genre field saying "Pilot Only"?
This relates to the old (poorly named) thread
http://www.tvmaze.com/threads/628/please-remove-this-was-not-a-series-it-was-a-1-episode-only-made-for-tv-movie
I don't think that thread came to any conclusion. It had a lot of posts that were not helpful.