Double checked this on my setup and it seems to be working ok for me (I’ve got a few Director's Cut or the Avatar Extended Collector's Edition in my library).
Is this missing for you in Plex Web or only in the windows client?
(This document describes combining Editions and Versions.)
When I redid the Edition tags, it worked. Either there was some weird cache thing before, or more likely I simply made a typo somewhere–perhaps the Edition tags were mismatched.