Hi Wrinkles, Chappell music has the copyright on behalf of the McPeakes and at first it was owned by the EFDSS, belief it or not. There were three Francis McPeakes, the grandfather, father and 'young' Frankie. The Corries verse is taken straight from Tannahill although it should read 'the deep glen sae dreary'. The Hirshman verse is not connected with the tradition of the song at all and is either taken from another song entirely or else newly composed. Stories about where it came from i.e. an old man in the pub, or an uncle have no relevance as to who owns the copyright. The Grandad is credited with writing the song or at least recording it for the first time hence the copyright ownership as the meoldy wasn't previously published before 1957.
The melody of WMT is the crucial factor in deciding who owns the this song as Tannahill's words are trad anyway (he died in 1810). My wife's picture of the whole family can be seen at www.richardandmimi.com/troubadour