Good news and bad news on this.

First, the good: I figured out that I had a latency problem with my audio playback. Found a workaround with another codec, and so everything is good now in Premiere Pro. Files have all been combined, everything is working smoothly now.

Bad news: the sync in the original files is all ****ed up and all over the place. For a few scenes the audio leads the video by a couple frames. Then there’s a scene where the audio lags by a frame or two. And so on.

Only choice now is to go back and fix the sync scene by scene … for all 9 or 10 hours.