Are "unestimated" and/or "non-estimated" correct English?

Solution 1:

In normal use, unestimated is not a word. Non-estimated may be syntactically correct but also doesn't really make much sense.

If you are referring to a industry specific term then potentially anything can be used despite being outside normal use. So it would have to be a word to describe a state — the state of not yet receiving an estimate.

Contrary to the other answer here, I'd say that both suggest the subject is estimable, but has yet to be estimated.

Solution 2:

Un-estimated, much like 'undo' or 'unwind', is conceptually the idea of reversing some action. Hence, if one were to have an estimate, for instance, an estimate of 100, re-estimated to 120, and then reversed (for whatever reason) to 100, that would be un-estimating the figure of 120. There is no other single word which conceptually matches this concept, as closely as 'un-estimate'. An explanatory phrase, such as 'the estimate has been reversed' is an explanation, not a term or word. On the other hand, if something has not been estimated at all, that would more accurately be reflected by the term 'non-estimated' or the phrase 'not estimated'. To use 'un' in this context, destabilised the assumption upon which all other 'un' prefixed terms are based on, which is one of reversal.

Solution 3:

Since it falls into the software area, I will venture an opinion - purely on a gut feeling.

Un-estimated sounds like it can be estimated, or should be estimated, but has not been estimated yet.

Non-estimated sounds like it should probably not be estimated. An example would be a project milestone, review meeting, etc. In oher words, does not need to be estimated.

Just my 2 cents from the software industry trenches!