JI Seed Compost is for sowing seeds; JI Cutting Compost is for rooting cuttings; JI No 1 Potting Compost is for pricking out young plants; JI No 2 Potting Compost is for potting on; JI No 3 Potting Compost is for established plants and shrubs; and JI Ericaceous Compost is for plants which cannot tolerate lime.

Also have look at this site where info above is from
http://www.gardeningdata.co.uk/soil/john_innes/john_innes.php

As Steve says. JI#1 has 1 unit of fertiliser; JI#2 has 2 units of fertiliser and JI#3 has 3 units of fertiliser.

That makes sense then, thank you!
That'll be why my fruit trees needed No3, they shouldn't need replanting in a hurry :)