Why do people believe that all the hair that has been kept alive thanks to fina/duta magically just falls off within 6 of stopping the treatment? It's not like the follicles are keeping track of how much the hair should've receded if you hadn't taken the medications. All that happens is that once you go off the meds your follicles will begin taking damage from the DHT again and recession will begin anew.
Concerning Ashton Kutcher I find it very much plausible that he could've lost just that much in 3 years. For one, because at that age the body doesn't produce as much testosterone/DHT and for two, because his twin brother (who I presume hasn't taken any meds) still has a fair amount of hair left considering he's been losing for 15 years