I lost a screw in type cap on my oil res a couple years ago. I am confident I hadn't screwed it in tight, if at all, so the blame falls squarely on Operator Error. Though the cap had the typical tether, it pulled out too, so the cap was well and completely lost. I noticed my boot was seriously oiled, which was the first sign of trouble. My pup and I seriously searched the area, but never found it. I was able to pick up a new one at the saw shop later in the day, so I didn't really lose much time. Had an oiled boot reminder for a month or so. Probably ran saw with no oil for a while till I noticed, but did not run long enough to damage the oil pump. Another lesson learned, and mistake not since repeated - yet!
And, of course I have also lost a bar nut once. While cutting up a downed pine tree in our church lawn. We moved all the wood, chipped all the branches, and raked the area but didn't find it. So, I bought two, one to replace the lost and one to carry in my saw box. And while walking the area a couple weeks later, I found the original. So, now I have two spares.
My perspective, if you haven't dumped a load of oil on your leg/boot, and lost a bar nut, you have sawed enough.