This is often heard in the debates of Congress, and is sometimes used by writers in the Southern States ; but it is unknown in New England. "There is (says an English friend) much affectation in the use of the words provenproven and strickenstricken among certain American writers and speakers. To labour, as some do, to raise old words from the dead, is not only not tanti ; but it shews, that the persons who use these exertions do not consider, that if they are in any degree proper, they ought to be carried out to a much greater extent than the parties seem to be aware of."
One marked form is, however, here to be noticed : this is the past participle proven for proved. The word is derived from the French, and in literary use has been inflected, until the present century, like all other foreign verbs, according to the weak conjugation throughout. But the strong participial form provenproven has made its way from the Scottish sub-dialect of the Northern dialect into the language of literature, and not only has grown common, but promises to become universal ; for it is employed by many of the best modern writers, and in particular, occurs frequently in the later poems of Tennyson.
But Luther Townsend, The Art of SpeechThe Art of Speech (1881) counters by including "Proven, for proved" in a list of "provincialisms [that] should not be allowed to mar the sentences of any one who aims at correct and chaste speech."
proved, proven. Four critics [including Theodore Bernstein, The Careful Writer (1965) and Wilson Follett, Modern American Usage (1966)] and American Heritage [Dictionary] object to provenproven as the past participle of proveprove: "The mine has proven worthless." Three others consider proved and proven equally acceptable, and both Random House [Dictionary] and [Merriam-]Webster regard proven as standard. Opinion is thus divided.
There is reason to suspect that those who declare for provedproved are taking their cue from Britain. ... Haggling over the propriety of provenproven vs. provedproved in a language like English, which is nothing if not irregular, is surely unreasonable.
It may seem silly to worry about using "has been proven" today, when as many people use that formulation in edited publications as use "has been proved." But it's worth observing that some readers continue to view proven as a mistake in that situation,—whichsituation—which may or may not matter to you. Once you know the history of the dispute, you can proceed with your eyes open and make an informed decision about which word suits your purpose and your preferences better.