As I will capture PAL laserdisc as well, because they have soundtracks in other languages than english (french and german), I could always replace the eventual missing frame(s) from the NTSC LDs with the ones from PAL LDs.

Correct speed: of course, the PAL soundtracks will be converted from 25 to 23.976fps, eventually the pitch will be adjusted as well, when it's the case - some PAL LD and VHS have the right pitch, but were rare at the beginning, more common towards the end of the formats, in particular for important movies like Star Wars.