Brian & John
I have access to 2 editions of GGG. The earlier definitely contains The Cambrick Shirt on p11. This edition is undated but was printed by and for R Christopher. It must be c1796 because there's a lot of rhymes added at the back by either Ritson or Douce in 1796. The other edition was printed by Christopher and Jennet of Stockton.

However, in Roy Palmer's 'Folk Songs Collected by Ralph Vaughan Williams' at page 31, Roy says 'The first appearance in print of 'The Cambric Shirt' was in GGG (1784).' The ODNR also backs this up.