I don't see any reason the refs should make calls based on what calls they made earlier in the game. if something's a penalty, call it
I absolutely agree with that, for the record, but that's not how this league has worked for a while (has it ever?). The rulebook is never called. If it was, McDavid would singlehandedly draw a half dozen penalties a game. Some Pens fan might tell me I'm whining - maybe I am - but if they called it by the rulebook there should have been a half dozen or more on the Pens tonight for what they were doing to obstruct the top line. There were guys hanging on the backs of Rantanen and MacKinnon. Should Landy's slewfoot have been a call? Absolutely, 100%. But given they somehow decided the Pens committed one penalty all night it's rather clear things aren't called by the rulebook, and so I don't feel badly about it at all.
I think "game management" plays a pretty big role in what's called and whats not. They didn't want to call anything on the Pens when the Avs were up 3-0, so they let the Pens get away with everything for the first 38 minutes; they don't like calling penalties in third periods, so they let both teams get away with everything; and they certainly don't want to call a penalty with a minute to go, so you can pretty much get away with murder, AKA Landeskog's slewfoot.