Quoting: rootferdukes
Ah, I was only considering average active roster size, i.e. just the days in the NHL column. Cap hit still counts on IR, but a roster spot opens up for a replacement, so using just NHL days to determine roster size shows you which teams called up replacements or extras after the deadline and which ones just subbed in their scratches to deal with injuries. Plus if you were to use NHL + IR to figure VGK's average roster size from 2018, you get an absurdly high number because Stoner, Grabovski, and Clarkson all were on normal IR that season, even though they were never active at any time that season.
Going by just NHL days, Caps had 22.39, 21.98, 22.63, and 23.01 average active NHL players on their rosters in 15-16, 16-17, 17-18, and 18-19, respectively.
NHL days is healthy, (including healthy scratch type players), count against the cam and the 23-roster limit.
IR days counts against the cap, but not against the 23-roster limit. That is why you can have over 23 against the cap, but still be below 23 limit on the playing roster. Your numbers are (might be, I didn't do that math) the playing roster, not what counts against the cap.
LTIR, SOIR, and suspension do not count against the cap nor the 23-roster limit.
Vegas and Arizona grabbed a few LTIR type players but put them on normal IR so that their cap hits would count but they didn't count against the 23-limit. Hossa would be another example of that.