So it’s a 145.012-68 (ie not even a 67). There very little chance this is an original caseback imo.
Obviously this is conjecture but I’d say a realistic scenario here is a genuine 105.012 that went back for a factory service a couple of years later and for whatever reason the caseback needed to be replaced. In lieu of a service case-back as there perhaps wasn’t such a thing, this is what was used.