I recently converted my lossless music to FLAC now that Windows 10 supports it natively. But when viewing these FLAC files in Windows Media Player, the year of the songs show up as "unknown year" despite having the year correctly labelled. I've noticed that compared to mp3 files, when you go to the details tab in the properties of a FLAC file, there's an extra tag option called "Date released" below the Year tag which when filled in allows the year to be displayed within WMP, although this is quite a tedious solution.
From what it looks like, WMP isn't able to read the Vorbis tag DATE. There's also a problem with the Artists name not showing up in the contributing artist section, probably for the same reason. I'm not sure how well WMP is able to read the vorbis tagging system but the ability to do so seems to be poorly implemented.
On a side note, there doesn't appear to be any standard windows media player FLAC icon for when WMP is the default media player, instead it uses the M4A file.