I follow some YouTube channels on classic video gaming (retrogaming). Several of these channels have published videos on a certain product that was hyped in the marketplace in the early 1990's as an amazing new gaming accessory but that then suddenly disappeared from contemporary discourse (e.g. gaming magazines) and may have never appeared on shelves at all. The channels seem to be in agreement that while the product was real and got canceled around the time of its scheduled release, the question as to whether or not it ever made it onto store shelves anywhere in the world (and made available for purchase by the general public) as a retail release is unknown.
To be clear, as a retrogaming question, my particular question is probably on-topic at both Arqade and Retrocomputing Stack Exchange, but I am more interested in the general case of "we don't know" or "nobody knows" claims.
If a claim about X meets general notability requirements (e.g. widely believed and/or notably claimed by a celebrity or other notable public figure), does it matter if the substance of the claim is not "The fate of X was Y" but rather "We don't know what happened to X"? If so, is it acceptable to ask "What happened to X?" as a question, or would we be limited to considering "Is it true that nobody actually knows what happened to X?"?
Another example of this could involve my studies of ancient tales that exist on the borderline of true history and legend. Historians generally define a border zone of varying width between events and dynasties that are clearly historical and ones which are almost certainly fictitious, with varying degrees of confidence assigned to events and figures within that border zone, but generally concluding with "we don't know if this was real or not, it might have been". Is asking about the "truth" of one of these events or figures in-scope? For example,
Simon Jones, the official city historian of East Podunk, Tennessee, claims [cite] that it is unclear whether King Varkoooi XIV of the Seventh Semi-Minor Dynasty of Neo-Pre-Post-Paleo-Classical Western Ruritania actually existed or was invented to legitimize the royal claims of the Restorationist Kings of the Eighth Semi-Minor Dynasty and/or the early Quasi-Regents of the Early Period of the postwar, pre-crisis, trans-Magdegonian Neo-Post-Paleo-Classical period of Western Ruritania. Did King Varkoooi XIV actually exist?