To illustrate, searching American Dad S16E01 will invoke Sonarr to search for S15E01. It seems to decrease the season value by 1 before parsing it to the search function, and it happens for all seasons except for S01 as it couldn’t possibly search for S00.
Screenshot: https://i.imgur.com/sjcb5YC.png
Sonarr Version: 2.0.0.5322