Regarding extra frames. I don’t have any of the scripts on the HDD anymore but I think I did reference it somewhere here in this thread. I believe it was 1 or 2 of the PAL releases and it was only ROTJ that had extra frames. There might have been 1 release that had the extra frame of the guy waving his hands while directing the droid into the back of the x-wing in the hangar in SW but I honestly can’t remember which release that was.

Regarding the black frames inserted to maintain gout-sync. Those were digitally created and should be entirely black. Also, I applied the limiter plugin to all encodes which sets the lowest pixel value allowed to 16, so with the script above you could probably set the global blankthreshold variable to 17 and extrapolate the missing frames from my various laserdisc releases. The black frames that should be in the film would contain dropouts/analog noise and should have a higher threshold.