What they all said - nice job on what had to be a tedious (yet rewarding) production!

Regarding public domain tunes, rights, etc., I've posted here several of our arrangements of songs in the public domain. In the US it is an exceedingly complex issue. But the bottom line and the most strict interpretation of the law is that if the song was published (sheet music) prior to 1923 it is most assuredly PD. After that it is considered not PD unless the rights were not renewed....and to further complicate things if the song was simply recorded that is considered to constitute original proof of ownership. I always look up the song via the Harry Fox Agency's song search feature. There are also several websites that list songs that are in the PD -- but even they offer caveats. If the song is attributed to a specific artist but has been recorded multiple times as PD or Traditional I think it is safe to assume that the rights are not owned by anybody. Of course you can copyright your version of any song that protects your arrangement.

What I've discovered is that many of the 1920's - 1930'a blues and even country/folk songs that I love have strong roots in African-American spirituals and field songs. Somebody may have copyrighted the song 70 years ago or more but it is obvious that it was ripped off -- in many cases nearly word for word and in other situations a verse from here and there.

And, even if you own a digital or mechanical license to record/sell a song it is still a "cover song" and would not be allowed on this user forum -- as I interpret all of this.