Why some footage uses dropframe and some are not?

Hello,

I have a couple of footage that I shot with an action cam. All the footage has the same frame rate and resolution. No paramaters were changed during shooting. I press the shutter to start recording, I press the shutter again to stop recording. Repeat a few times.

When I import the resulting videos into DaVinci, the media panel (attached) indicates that some of the footage is marked as using dropframes (DF) and some don't. What gives?

Thanks.

NTSC was originally 30 fps, when color was introduced they needed to change the frequency to minimize interference so it was changed to 30 * 1000/1001 fps.

The timecode however never changed, so then some "genius" came up with the drop frame concept. And here we are in 2024 still dealing with it.