Hi Des,
I am only a novice, as many will know, but would think that it infers no rights to the song itself only the medium on which it is cut.In other words the acetate is yours to buy and sell but not reproduce without permission. Intellectual property laws, mean that the writer always owns the song unless they sold the rights to a third party (possibly a recording studio or publisher or record label). Even in many of those cases there can be a cut off period where it reverts to the original writer. The Presley estate was an example where the songs had a finite period of sole use and reprodcution by the Presley estate only or by contract to them I believe.
I am no expert but did do a little digging on it last year. I am positive there are many more enlighted than me that will correct any misconceptions I may have on the matter.
Mark.