Guess i need to go through every member who is using cannon contracts on custom bios and revoke their rights to use them.
Like Leaf, Wesobi, Pervy, etc etc.
Once you learn a cannon contract, you can use it on your bios unless there is a restriction of said bio that makes it impossible to do so. For example. Orochimaru can't summon toads... Tsunade can't summon snakes. Etc. Other than that, you don't lose access to the summoning just because you change bio. This is so because you can learn and use the cannon contracts on custom bios. Unless that is to be revoked, there is no sense in losing access to said contracts once you drop the bio. Also, note that if you make an Orochimaru bio, you get the signing of Snakes auto and you need to learn the summons but you can only do that if you have a summoning contract free slot. If you already have signed 2 contracts, you can't sign that one.
What you say is that basically Cannon contract = Cannon Bios only, which isn't the current case, regardless of it being right or wrong. The truth is that it doesn't matter. The way it is now is like that.