The official naming schema for multi-episode files is Show Name - sXXeYY-eZZ.ext, where XX is the season number, YY is the number of the 1st episode in the file and ZZ is the number of the last episode in that file.
With the latest beta, Plex have added support to drop the leading e for the index of the last episode → Show Name - sXXeYY-ZZ.ext.
It’s still the same multi-episode handling… clicking each of the episode items within Plex will play the full file; playing the file will mark all included items as watched.
See “Multiple Episodes in a Single File” in the related support article:
https://support.plex.tv/articles/naming-and-organizing-your-tv-show-files/
There’s a feature suggestion discussing an option to show such “multi episode files” as a single item in Plex, aggregating the information of all contained episodes.
