Just jumping back to answer this
Technically it could be in all situations, but when it's usually talked about people refer to even strength or even strength close situations. Unsurprisingly, teams have higher PDOs when on the PP than the PK, so teams that spend a larger percentage of time up a man as opposed to down will have higher overall PDO (which is one of the reasons the all situation PDO doesn't mean as much).
Anyway, moving on from PDO because I could spend far too much time on it and it's really a topic for another thread.
This is one of the big reasons I was excited for the shot quality project from Chris Boyle and why I reached out to him to see if his data was public. Unfortunately it wasn't, although he did say "not at this point" as opposed to "no", so it's possible he'll eventually release it.
Intuitively, we know that certain shots are harder to stop than others, the problem is statistically quantifying that effect. Under the standard corsi/fenwick model, these effects are ignored under the guise that over large sample sizes the effects will disappear. In other words, the claim is that shot quality, although it exists, isn't controllable in a meaningful sense, but is rather a fluctuating thing based on luck inside of a game.
Although even the most ardent of supporters of corsi/fenwick will agree that games like MA Fleury had on Sunday (where the stats say he was terrible, but the eye test said he was actually great and the team was hilariously bad in front of him) will happen from time to time, a team can't really control them enough to matter in the statistical sense.
That's what we're really trying to dig into in this thread. Is that viewpoint correct? Or is the claim that the Leafs (among others) have "figured out" a way to maintain higher quality shots than their opponents (through either skill or system) correct?
It's worth noting along those lines that we need to be speaking the same language. Go beyond whether one side is right or wrong about the fate of the Leafs in the standings and instead focus on what's actually happening and how it relates to the numbers, not the over reaching claims of some posters. ie. If one poster says "corsi says the Leafs should regress" and then the Leafs play 7 shootout games in a stretch of 13, winning 5 of those shootouts (like they did earlier), you could easily say "hah you were wrong". However the problem is that doesn't actually advance anything. The underlying claim, that the Leafs were outperforming their corsi, remains addressed. The Leafs found a way to earn points in the standings without beating a team in the "usual" way.
Now, that's not nothing, however if we're discussing corsi (as the thread topic suggests) then shootouts are irrelevant so we're comparing apples (performance in "corsi situations") with oranges (overall team record). Claiming that the Leafs winning a shootout means they proved corsi wrong, without actually paying attention to underlying numbers, is just as simplistic as saying that corsi dictates they're likely to have a worse record than they do. Both are simplifications and generalizations. The typical Corsi model does not imply the Leafs overall record will fall, it implies that the record in corsi situations will fall. Similarly winning a shootout doesn't mean corsi is wrong, just that the Leafs were able to win outside of corsi.
Hopefully we're all on the same page after that. So now we can look at corsi specific situations. More specifically the most relevant are corsi/fenwick during even strength and during 5on5 close games (all tracked on extraskater.com).
Earlier in the year I compiled 5 and 10 game rolling averages for Goals for %, Shots for %, Fenwick for %, and Corsi for % for the Leafs to look for some trends. I just updated them and there's some things worth noting.
That's the 5v5close, 10 game rolling average, through the game on 3/16 against the Caps. The averages are weighted based on time spent at 5v5close (ie against the Caps there was only 12 minutes of 5v5close play, compared to 48 in the Rangers OT game in 3/05).
As you can see, shots, fenwick and corsi all track pretty close to each other, there's no meaningful different at any time in the season. However goals has a massive swing. At the beginning of the season the Leafs had a crazy goals for rate during close games, approaching 80% for one 10 game stretch and basically at or above 60% for 20 straight games.
Then, around the 25-30 game mark their luck started to change and the goals for starts to fade back down to near where corsi and fenwick are. That's where the "regression" really happened. During that time is also when the Leafs went on the stretch of pushing a ton of games into the SO and winning many of those, which is why the overall record doesn't match the "corsi close" record.
Recently the Leafs goals for % has again increased which begs the question: Why? Is this random luck fluctuations, or is this driven by something (players returning from injury?) Unfortunately I don't have enough data to determine this