Hi Andrew
This is how my friend John Bentley gets around it , all three matrixces are transferred to a very heavy watercolour paper and is some of the prints a gelatin coating goes over which would solve this.
Sandy King as far as I have seen and I have seen a lot of his prints does not put a coating on the prints as he wants you to see the relief and its really obvious to the naked eye.
I met with Mark Osterman years ago at GEH and this topic was brought into conversation whereas he stated that very old Transfers 100 years plus were in some cases flaking and required conservation efforts, I would imaging a coating of gelatin would be that solution to the problem.