Quicktime Player Framecount Discrepancy

I'm having issues with inconsistent behavior when previewing quicktime movies' frame durations.

I have two videos that have inconsistent duration issues by one frame, in opposite directions:

The first video has a duration of 332 frames according to the quicktime player.

The second video has a duration of 50 frames according to the quicktime player.

When I preview the last frame of each video, they exhibit different behavior.

Both videos are rendered as an H264 Quicktime.

As you can observe, the first video stays at 332 when previewing the last frame, and one advances to from 49 to 50 when previewing the last frame.

When these quicktimes are compiled into an edit with other videos, the total duration for the first video is 333 and the second video is 49. That being said, it seems that all visible frames are still visible for the exact same duration as the individual videos. When I go frame-by-frame, I can see frame the burned-in framecount 332 for two full frames, and for the second video, I can see the burned-in framecount of the first frame and 50 both visible.

Am I not understanding something here with the way quicktime counts frames?

As an additional note, my theory is that at some point the first video was processed/rendered at 23.976 FPS and then re-interpreted at 24 FPS, causing a frame to appear as a fractional frame, causing Quicktime to either choose to extend this frame or cut one frame off in it's count. I may be wrong, so please let me know either way!

Thank you.