So are you suggesting that some callsigns could start with several zeros? Inputting leading zeros used to be possible but served little use. Often nowadays aircraft callsigns have a mix of numbers and letters, primarily to avoid callsign confusion when two flights occur at the same time with similar callsigns. Having used R/T for most of my working life I don't recall too much difficulty with callsigns whether they had one number or several, e.g. Clipper One through to Air Force 48913..