One more thing...we only need to concern ourselves with vehicles that "disappeared" in the 12 months following 12/23/1974. Any VIN# and/or registration not retired legally, by title transfer, or by salvage, or reported stolen - every vehicle that went off the grid in that following 12 months was owned by someone. That list is the one I want - to compare to the one that should be in the case file.
You would probably first have to make your own list of cars owned by people connected to this case, and cars to which they might have had access (via family or friends). Unless LE made a list from their own research and not simply from what they were told.
Not so fast! That car could have been hauled out over 44 years for a variety of reasons. Underwater hazard, etc. The Army Corps has responsibilities. I need their list.
I'm the first to think water burial whenever a person and a car go missing. But another possibility is a car becoming part of the landscape on a ranch or farm. In my rural area, wrecked cars are sometimes hauled in and used in a pasture for a livestock windbreak. And some ranches have a metalyard--like a boneyard, where animal carcasses are discarded, but with all types of metal discarded in a heap, sometimes in a sinkhole, sometimes over the edge of a draw, etc.
Forty years ago, my spouse and I did that with an older car we had, not worth much so we had just liability insurance on it. Wrecked it, bent the frame, among other "injuries." Hauled it to a rancher friend's place, where it remains to this day. And I think the title is still in our files. No report made, and no one ever went looking for info on the car. Friend has since sold the ranch, and I'm sure the new landowner has no idea who left the car there.
Of course, there were no bodies in the trunk, and if LE ever went looking into the car's history, our names wouldn't be hard to find via the VIN and last registration.
But in the meantime, there it sits.
So if a car is indeed missing from someone connected to this case, some in-depth research may be necessary to find it.