My appendix in the latest edition mainly concerns material from the subsequently-discovered MacLean-Clephane manuscript, among other things, so it has some nice music that's not in the first one. But the only mention of Carolan's Concerto (I have no reason to dispute Dr. O'Sullivan's findings, cited above) in this new section is the inclusion of the modern version of this piece as it is now played and heard, for the sake of completeness (and also not to disappoint any musician who looks for it in this book). The earlier one is pretty similar in the "A" music but differs somewhat in the "B" music.

Donal O'Sullivan's biography has never been surpassed for scholarship, and is still the definitive source. (He is no relation to Mícheál Ó Súilleabháin, BTW.) I believe you can get the updated modern edition from Simon Chadwick - it's published now by Music Sales Ltd. in London and IS still in print.