Modern Stamp Design Process -- Who Does What?

I collect US stamps with a military or space theme pre-2001. I want to include information on who designed and engraved each stamp. For pre-1948 stamps I have found an abundance of information from several sites (Arago, Stampsmarter, etc.). However, from about mid-1980 on I have started seeing new functions other than "engraver" being mentioned; such as modeler, typographer, illustrator, even art director. I assume that this is because most work is now down on a computer and nobody actually engraves a printing plate anymore.

So, regarding stamp design an production of printing plates for modern stamps, can anyone tell me who does what?

Any help would be appreciated.