The corpus of Latin literature, while large compared with the corpora of many other classical languages, is also more or less finite; in many periods (e.g. classical) it represents some but not other registers of speech. Cicero's speeches are great examples of rhetorical style, for example, but they neither represent nor profess to represent colloquial style.
Take the word sícáre, for example, which I made up the other day (thinking it was a real word) as a back-formation from sícárius, "assassin." As far as I know (and as far as Lewis & Short tells me), the verb sícáre isn't recorded as having been used in Latin. But it doesn't seem impossible to me that there could have been a verb sícáre that nobody happened to write down.
Obviously, there's no way to prove non-existence of something—we can only prove or fail to prove its existence—so there's no way to answer this question definitively as a matter of epidemiology. But as a practical matter, if something isn't attested, should we assume it wasn't used?