I wish I had more concrete information, but I remember hearing about one police department treating bodycam recordings in public and in private places differently for this reason. I imagine the officer would tag it when they left their shift or offloaded the footage.

In general, I've heard reviewing the footage is a huge undertaking and an unexpected burden. I wouldn't be surprised if, like many backup systems, they're not often tested and found to be insufficient when they go to pull a video...but, then again, they also deal with evidence which has similar requirements.