To the OP's question, there was an article or series of articles published in Handloader Magazine at a much earlier time where the same hulls, 12ga. I believe, were basically loaded until the mouths were shot off or so sorry they would no longer hold shot w/o some added closure devise and both pressure & velocity was measured at each loading. If I recall correctly, there was some degradation of attained velocity, but it wasn't particularly significant even when it was the hulls' last usable loading and pressure was highest on the first reloading as could be reasonably expected.
Pressure & velocity are two dif. animals not related to one another in any mathematical sense as has been noted here and other places multiple times and will only say to not lose sight of that fact.
In my own experience, the yellow 20 ga. hulls get uglier looking [dirty] quicker than the other gauges. Purely a color thing, IMHO, but the hulls are easily enough acquired, so I toss them when they get ugly, tho they would continue to break targets for more reloading's. Mostly the only dif. between once loaded and multiple loadings for skeet ranges is your fingers get dirty along w/the hulls if you don't wear shooting gloves. I don't notice that it affects the numbers of targets broken when the gun is pointed correctly. Dirty hulls breaking as many targets as new ones. Head games are a dif. horse; if you THINK it makes a dif., it probably will and it need not be based on fact.
Phraseology & word choice aside, whot Wonk is saying is the essence of it; don't get too caught up or caught up at all w/meaningless and often wrong minutia as tempting as it may be or as Joe Friday was famous for saying, "Just the facts, Maim."
And please don't read into my remark(s)anything snarky, no intention in that regard exists whatsoever nor trying to refute correct math or that the 96:1 rule is not a fine one for rational limits. It is, but it is also too stout for me were I to shoot many rounds in a day's time. And there is no connection to that and the OP's question either, unless I misread it.
