If a Paratext 7.6 user creates Notes on one install, and then creates Notes on a different install (without first having done S/R on that second install), should any problems be expected in syncing the results afterwards?
Assuming that by “install” you mean a different machine and they use the same Paratext user for both machines, then that situation should work fine. The notes file should merge together and no merge conflicts should occur.
Would (or could) that be different after there has been a sequence of events as follows?
I would expect it to still work fine in that case (which I assume is this case).