This is not authoritative advice from CCLI. Please check your CCLI license agreement or confirm with the CCLI representative in your country for any questions regarding copyright.
Our understanding (provided you are not recording your service) is that you report each song just once – in the year of the first time you actually use the song. Treat it as if you typed in the words yourself, as that is what constitutes a ‘use’ (or reproduction) of the song.
Tip: Use the playlist/running sheet export to CSV feature to keep a historical reference of the songs you use.
If you record your service (ie. to tape/CD/DVD), you need to report that as a duplication each time – and any copies you make of that recording as well.