Kept reading your post and had to point one thing out, those saved frames in DeepSkyStacker are not the same as real exposure time. DSS only keeps what you actually fed into it, so if you threw out subs because of clouds, planes, or bad tracking, that time is gone. I have the same issue, my folders are full of junk I never stacked, so my real number is way higher than what DSS shows. Also the "same galaxy from four backyards" thing, that is what gets me, not the hours but the fact that you can add another 10 hours and barely see a change. So yeah, 100 hours tracked is a lot, but your true time under the sky is probably even more, lol.