I don't think you should start by assuming what I "seem to think" or not — the fact remains that the term does appear at least once in the glossary, so if you were unable to find it, then you might need to refine your search technique
1) always be sure to also search reverse language pair — this can be immensely helpful!
2) always search for just the root, uninflected form — if you search for 'les tags' you are unlikely to find it; but if you search on just the root 'tag', then you ought to have found it with no problems.
Here are 446 results — not all of them relevant, of course:
http://www.proz.com/search/?term=tag&pairs=my_and_reverse&la...Perhaps there were too many for you to wade through?
peer agreement (net): +5