I just went through an example qualification for my BJCP class. It was fascinating.
A class mate brought PU in brown bottles that were just crazy with diacetyl. I am more or less blind to diacetyl and I immediately thought the host had dosed with popcorn butter. It was off the chart... a weird artificial butter note and a really strong mouthfeel slickness. I came home and cracked a fresh can of PU that still had a very low diacetyl note, but was very classic Urkel... freshness, high Saaz-y hoppy-ness. But I could still taste that diacetyl three hours later. It was pretty strange.
My class admin and I visited a brewpub that serves PU on tap. Three ways - all based on foam. We had a flight of the three. Only the "normal' pour had the butter element. The rest were restricted to half foam and all foam - and the D levels were tremendously reduced, while the bitterness increased. It was a great experience!
I think that with PU, the distance between oxidation, light struck and D is the variation that I have seen. I love Urquell in the can, but will pass when I see it in the glass. Will be thrilled with it in a properly cellared firken... or a properly maintained tap setup.