As I say, MS Windows (Windows 10 at least) recognises MKV PART_NUMBER (T=60) and displays it as Season number (Windows property: System.Media.SeasonNumber).
Mp3tag's TVSEASON field displays in Windows as Season number when used with MP4 files, so I think it really ought to be mapped and working properly for Matroska video (MKV) too.
Let me know if any more info required.