Hi Pete. As producer of "Unearthed" I too had heard of the Knaresborough tapes, but couldn't track them down!
Mind you, by that stage in Nics career, the performances were all pretty similar, mainly because he had played all the songs so many times!
I've lost count of the number of "Allandales" I've got...(all of which arrived with a letter saying "Don't know if you've got this....!")
One day, If I get demented, I might load them onto the computer and when the chorus comes around have multiple Nics singing, taken from all the versions! It would be an interesting experiment...and would probably work! For Videos of Nic singing with son Joe at the QEH earlier this year, there are a few camcoder examples on YouTube...Go search. Dead emotional.