Nobody "sweeps" for bogus cameras AFAIK and I don't know any method of doing so. 

Once upon a time, you could report speed cameras through the app. This led to Central London looking like this back in 2012: All the brown ones were app-reported and not yet approved. Removing camera reporting from the app cleared a major headache for editors.

So any new cameras added are only by editors - who generally mean to add them and don't have the opportunity to get them in completely the wrong place as with the app.

I should also note that lock < 4 is not wrong. Our locking policy on cameras is to map them to L3 minimum, but higher if the lock on the segments is higher. It just happens that practically every road it's worth installing cameras on is busy enough to be auto(4) or higher.

There really isn't a lot of changes in cameras, compared to roads. Most cameras stay there nearly for ever and not a lot are being added. If you see a L1/L2 camera, check it out. It may well be genuine, in which case you can adjust and uplock as appropriate.