I'm sorry, I must have misread your post...You say there are 3 different suppliers involved? Are they all PPG suppliers in your area? Or are they shops from different area's? If they are, are their jobber stores owned by the same person?
I just looked at some Deltron I had left over from the days when we could still spray it...(a pint of black that had never been opened). It's not reduced and it looks like it would be tough to get out of the gun and get it to lay down properly without reducer, let alone flash in 5 to 10 minutes.
Do you know of any body shops in your area that use PPG and have their own mixing system? If you do I would take a sample of what your buying to the shop and get their opinion.