Dell OS10 is very different from Dell OS9. Would it make sense to have different tags for them?
Hmm. Currently, we've got two questions mentioning OS9, and three explicitly about OS10. I'm afraid that doesn't really warrant tags. There are 86 questions tagged [dell], could these potentially all be tagged either [os9] or [os10]?
Still, if you've got sufficient reputation (not sure how much, sorry) you can go ahead and add the tag to a question, creating the tag. Please make sure you also add some explanation to the tag wiki.