It happens also when I attempt to get parts for my 1960 VW with a 6 volt system originally that now has a 1962 or so Motor with a 12 volt system. Forget counter dudes and dudettes, try transposing part numbers for 1961 and above for my 1960 which, BTW, was a bit of a red headed step-child when talking about model years for VW. All separate, specific and mostly unique parts for 1960.
My 25yo son runs an auto parts store and an exchange with him would be a lot like the Op's example 2. But, it's a small town store owned by a regional chain and he actually knows what the parts do that he sells.
He worked at Autozone some years ago when he still lived at my place. He had daily funny stories about not just the customers but the employees. We still call the place ReturnZone.
Bear in mind, even some of the experienced guys and gals go into auto pilot from time to time. I once asked a counter person I regularly deal with who knows their stuff, for a clutch kit for whatever I was working on at the time. First question from the parts person, "automatic or manual?". I stood there silent until they realized how ridiculous the question was, we both chuckled and proceeded with my parts order.