from my short experience in collecting non R1 discs , if the disc is region locked, there will be a disclaimer that doesnt allow the disc to play at all. on my region 0 PAL discs, it plays the title screen and even the menu screen but wont play the episodes themselves . of course not all of them...
“The unfortunately incorrect fine print saying 'Region 0'...when I first got my set, I tried playing it on one of my R1 players, and it was a no-go...too bad, but this is a Region 2 LOCKED set, and thus you will need a region-free player..”
This may be correct as some sets are Region 0 but PAL...