I think I have an idea what the third fs patch for 19 fw does and when it matters
so if I only have the first 2 patches, things work fine, no problem, xci will run. but if you do a corrupted data check on that game, it will say it found corrupted data (normal I think)
on fw 10-18 we had only the first two patches and it was fine even if I did a corrupted data check, it would say it found corrupted data of course but I could still just go back to the main menu and run the game, or at least I dont remember that ever being a problem?
on fw19 if I do a corrupted data check but I only have the first 2 patches, then I can't run the game anymore no matter what. it will appear to run, go into the black screen, then instead of loading it gives the black screen with the [!] and the error message that the game could not run. the os remembers that corrupted data was found and that the data is invalid, and will refuse to run the game until you reinstall it
but if I have the third patch, I can run corrupted data check on the game, it will say it found corrupted data (again, normal I think), but I can go back to the main menu and run the game and it works fine
so if you avoid doing the corrupted data check on installed xci games, you are fine with just the first two patches, but the third patch will be needed if you ever run the corrupted data check
so it's probably not an extra check against piracy, but rather an extra check to prevent actually corrupted games from loading (because of corrupted sd card or whatever), but because xci installed as digital gets seen as corrupted data, it ends up affecting that too