This is a weird one...
I would imagine using \ in any field might cause problems with any editing or playback software.
That being said, I have never done so, but I've encountered a bunch of albums in my collection that have multiple years separated by \\ in the year field/tag.
I think it's to denote the original release date vs. reissue, etc.
For instance, one album has 1990\\1988 in the year field for every track.
If I add Year to the columns, the only date shown in the Year column for this album is 1990.
If I change one track to 1990\1988, both column and tag panel show 1990\1988 and I can filter using: year HAS "".
How come \\ will show in the tag panel but not in the column?
Is there any way to filter for a double backslash?