If you are referring to the theories of the 1980s and 90s and you also have only one theory from 2000, what do you say:
"My paper is a criticism of the theories of the 1980s and 90s and of one theory from 2000."
I find this solution a bit awkward.
"My paper is a criticism of the theories of mostly the 1980s and 90s." ('mostly' indicating here that there may be theories from the 21st century) - perhaps it is even more awkward than the first sentence, anyway
Any better suggestions?
Are you covering ALL the theories for the 80s and 90s?
If not, redrafting is easier.