Oil system myths

The first small block I ever helped build was a late 70s 360, and during assembly (I was about 14), I asked why there was no gasket between the pump and rear main cap. Dad told me he had never seen one (mind you he worked in a Dodge dealership in the early 80s through the 2000s) and swore that Chrysler never used one from the factory on small blocks. Is that true? Who knows, but it's interesting to me why they might use one on engine A and not on engine B. Maybe they were there in engines that the mating surface(s) weren't machined correctly?