Well here's my 2 cent:
We know that wakizashi went to war, but that the standard was a katana. We know that some wakizashi were custom fitted with properly proportioned koshirae. We know that some soldiers had money, and others did not. The variation in sword quality, and components, clearly displays that. ...My guess is that these wakizashi in not proper mounts are solider put togethers.. Family wakizashi with standard Gunto koshirae purchased pre made (probably cheaper than having your "uncommon" wakizashi custom mounted at the time).