That's why I tought that 9 is impossible... cause usually was Vialli number.
But maybe he had a "proper number" like 4 Baggio was 10, Vialli 9, Ravanelli 11, ecc... Anycase it's very difficolt to find out which one it was the first he weared.
The only way it will be to figure out wich was his first match and to find a picture or a video about this match...