Accounts system on N9 is tied to your simcard. You can have up to 7 sim cards in the same device to share same accounts -- as long as you have enabled device lock code. If device lock code was enabled before you have created those accounts, then all those simcards would have served as additional locks for Accounts store while device lock code would be your master lock key. The 7 sim card "limitation" comes from underlying technology albeit we could have expanded that to 32 but this was decided not reasonable case to fork established open source project (encryption of block level devices in Linux kernel).