So I ran into some more issues with airdate based series. 
1) Season search does not always work. Newznab wants the 4-digit year for the season and not the trakt season number. The season as it is now does not contain year information like that. I can aggregate the episodes to find this information though.
2) The airdate string matching can simply be off by a day. I wonder if there are some timezone/UTC here issues or if this is a scene-release vs trakt problem. In either case using the episode title would help here too unless you know of another way.