It does make a difference. DVD does not allow ntsc & pal to be mixed together. Thems the rules of dvd format. What happens is that those who live in pal format countries have players that can also play ntsc format.

The resolutions are different. ntsc runs at 30 frames/sec & pal at 25 fps. But ntsc has a smaller vertical height than pal (also the pixels run vertically whereas pal are horizontal - pixels are rectangle for tv, not square.) For pal the height is 576 whereas for ntsc is 540 or 480 I can't remember. So ... open them in quicktime & check their aspect ratio to see which ones are the highest compared to the lowest V's length. FPS is also a bit of a give away, unless the encoder chose 30 fps for pal which would seem a little strange!