This sample is deceptive. You can't have a list of "the 2017-2018 (season+ playoffs)" and then have there goalies that didn't play in playoffs this season, Antti Raanta, Subban, Lehtonen etc.. their sv% is not affected by their PO performance, they didn't play any games. So you shoud look at 2 samples, regular season for starters(50 games min) alone and just PO.
I had to make a decision. I didn't want to include several years back, and I didn't want to do the playoffs only (<31 goalies). Playoff games are statistically a marginal part of the whole year stats, including them to season stats doesn't change the percentages much.