Reg,
it sounds indeed like a very good method you have chosen just to let the sprayer mix an approach based on the stuff he is familiar with...and afterwards you can decide and you personally like it or not.
This way to create or define a colour is probably much better than having a given tone of an original car which can perhaps not be recreated so easily with other than the original paint ingrediences of her time.
What I have learned is that one even cannot say i.e. that old school paint looks better than modern ones. More important is, that the sprayer is very familiar with the method he is doing, regardless if his paint ingrediences are older or more modern ones.
