Is the "adoptable" tag useless?

I could’ve sworn when I shared some works that were intended to be adoptables (designs that other people can buy to use themselves), I tagged them with “adoptable”, but now I can’t seem to find it. It’s not aliased to “invalid tag” either. Derpibooru and Furbooru allow the use of this tag.
Is it regarded as useless here and I should never use it again?

I have nuked the tag, yes. Based on my conversations with them, I’m fairly confident Pup will back me on this when he reappears. No doubt the only reason the tag is not blackslisted (these tags cannot cannot be aliased, because they cannot be entered/created at all. Trying to apply them will have the software silently remove them) is that the blacklist is based off the tags used on e621.

Anyway, point is that them being adoptable is no more relevant to the image’s content than whether they are commissioned art or not. If Furbooru or Derpibooru want to allow this sort of advertising (which is the only justification for this sort of tagging), that’s their business.