Comparing different versions of the OS (Mint/Debian) and apache (2.2/2.4) I found that file names, content (what is in which file), order of statements in files, etc. can an will change.
However basically the functionality more or less remains the same. It's sometimes just confusing when comparing files from different PC's each with their own version of the OS and web server.
Regarding your "problem": could your installation of OwnCloud have something to do with it?
However it does not really matter to which log file Apache writes. Just use what Apache serves you.
I'm convinced your approach will work for you.
Maybe just search for "/cops/ " (space is intentional or "/cops/$)" ) instead of "getJSON".