Soundreef manages rights for authors and publishers who register songs in which they've got ownership shares, set through private agreements with all other rights-holders included in the chain of ownership.

Therefore, you cannot register songs in your Soundreef account to which you don't own the rights; infact, in this case, we strongly recommend you get in touch with the authors/publishers of the song as that's the only way to avoid a copyright infringement.

In addition, the Copyright Act (Law 633/41) doesn't provide a copyright component to the arranger(s) in arrangements of already existing works, except for agreements with the right holders (if they're still alive) in which the "value" for the creative contribution of the arranger(s) is specified.

Specifically for public domain songs (folk music/classical music), there's no rights holder (author/publisher) with whom a "value" can be agreed for the arrangement, so it wouldn't be possible to determine the actual copyright share, and it wouldn't be correct to assign the entire share as if the arranger were the original author.