Given something in a state of not having been validated or invalidated, its validness is, as yet, unknown. Can it be said to be unvalidated? If not, what is the proper term?
Those who say unvalidated (never having been validated) is "not a word" are simply being prescriptive, outdated, and pedantic. It's been used increasingly over the past century (the chart represents a total of 34,000 instances in print).
I don't see any problem at all with the word, which is clearly distinguishable from invalidated (having been been checked and failed validation). If OP wishes to avoid unfounded allegations of illiteracy though, he might wish to consider unverified as a less contentious alternative.