Normally pressing the event button give you 1 saved file, at least with cameras using a memory buffer, so you get xx seconds ( what are in the memory buffer ) + some time after ( this can be different from brands & model cameras.
Other brands / models deal with events on a segment basis, so say i press the event button on my SG camera when i am 40 seconds into one of the 3 minute segments i have set my camera to use, well then i will get the whole current 3 minute file + the previous 3 minute file locked away in the RO folder + a picture from the moment i pressed the event button.
On the other hand if i am 2.5 minutes into a 3 minute segment and press the event button i will still get the current 3 minute file locked away in RO but i will also get the next one, so again 2 X 3 minutes locked as event in RO folder.
Double that on my SG9663DC as it is a dual channel system so i get 2 X 3 minutes from both the front and rear cameras so 4 X 3 minutes in total covering the same 6 minutes in time.
I much prefer this segment basis VS any smaller buffer, cuz you don't need to hurry to hit the button to get the event in the event recordings VS if it is a buffer camera and you wait for XX seconds more than is in the buffer, the event will not be in the locked down event file / files, but in among the regular files and so still prone to overwriting.
I now use the event button for things i want to share, and then let a month or so of events scumelate in the RO folder, before i pull the memory card and make a compilation for my YT channel.