I recognize those.Those are neck plates from a Fender bolt on neck acoustic guitar. That's all I have ever seen them used on. Here's a picture of a vintage Malibu model acoustic.They were made from 1965-1971. Might have also been used on some other acoustic models.
As to the Fender acoustic serial numbers, here's info from the Vintage Guitars Info site:
All Fender acoustic flat top guitars have 2 screws in the pickguard, 6 on-a-side tuner configuration (except the Classic and Folk), and a bolt-on neck with a metal neck plate on the back. For the most part serial number follow the electric models. BUT in some cases, they do not. The year information here should be taken before the serial number. That is, if the serial number indicated 1956 and the model info says it was only made from 1965 to 1971, then believe the model information!
So, the neck plates in question in this thread fit in that "BUT" category.So far, I haven't been able to find any evidence that those were used from the factory on a Jazz bass or any other Fender electrics, so I can only assume at this point that some previous owner stuck it on the bass because they liked the look of it.
Edit- Here's another example, a 1968 Palomino acoustic.