This is the way that cyclone identifying works at the WHC.

If a tropical wave is uncertain about becoming a tropical cyclone, it is given an identifier designation. This usually consists of a letter relating to the basin, and a number that is how many cyclones have been identified in the season. After this, and it is near certain that it will be a cyclone some time in the future, a cyclone is given a "just-in-case" name. This is used if the cyclone reaches tropical storm strength, but is not officialy named by an agency. Once a cyclone becomes a tropical cyclone, it will be given an advisory number. This is the number of cyclones that reached tropical depression strength this season.

Take Bingiza as an example. It was identified on December 22, at 20Z. It was identified as S3. It was expected to become a tropical cyclone, and was given the "just-in-case" name Boron at 02Z, December 24. It became a tropical depression on ???? and was numbered as SI032010.