31 May 2021: APP 1.083-beta2 has been released ! APP 1.083 stable will follow soon afterwards. It includes a completely new Star Reducer Tool, New File Saver Module, Improved Comet registration and much more, check the release notes here!
I notice that after stacking a night of data, if I take that FITS file and load it into a new instance of APP it remembers how much data is in the file. Would stacking 2 suck files together give the same result as would stacking all the lights from scratch?
Not exactly, theoretically stacking frames together is better, but if you have enough data per integration (>40-50 frames), I personally don't see much difference anymore and it is a way to combine data for sure.
Ok, I had been stacking master light frames in APP for quite some time now and never run into any problems I was just wondering verifying that I wasn't unknowingly shooting myself in the foot.
You can always run 1 test for yourself, that's the best way to convince yourself what, if any, difference it might make.