Great Planes will tell you there is no difference in Monokote. I will tell you thats BULL!
I have many new rolls of monokote from the early 80's. I can take a roll of the old white and apply it with no problem at all. When I try to use "new" white, it isn't even close to the same stuff. Different shrink rate, different thickness and different tolerance to heat.

I switched to buying Ultracote a long time ago. If I need fabric, I am really fond of Nelson's Colorfab.