There are the tags 3, 4 and 5, for images having these single digits written somewhere. (notably, they serve virtually the same purpose as 2002, 2003, 2004, but the four-digit ones apparently always represent years)
Should the tags 0, 1, 2, 6, 7, 8 and 9 be used for the same purpose? I think they should.
They are all empty, except for 7, which is currently the name of a character. (And the tag 3 was an artist, in the past.)
^ do we have such policy? i've encountered some like texts or short phrases printed on character's shirts or paper or somewhere in the posts. it usually appears to be trivial but i leave it out because some are made by higher-level users. if those are truly unnecessary, i might start hunting some of those tags again.