Buy/sell reprints of jukebox manuals or PARTS legal?

[31hobbies]

Newbie here. 

Reprints of service manuals, schematics etc of jukebox manufacturers that are no longer around can be seen for sale worldwide.  Just curious about copyrights of these old documents.

For the music entertainment industry, even with hundred-year-old classical music work, it depends on the process which the piece is recreated to the final product: CD, video, online streaming, live concert..etc. 

Some reprint sellers claim that their reprints are legit, others just won't reply.... 

So how is buying/selling old jukebox parts OK?

I carefully worded this post so as not to get my host forum in legal trouble. 

[jukeboxmarty]

A large portion of the technical material published by the original manufacturers was not specifically copyrighted or the copyrights have since expired.

Some of the re-prints that are copyrighted apply to the specific compilation of materials; the original materials have been in the public domain for years.

-Marty