NikT: (e.g. worst case scenario: LSP submits a disconnection order in error, which prevents the reassignment going through, delays everything, & requires a reconnection)
OP was probably worried that would happen which can mean period without internet, which is messy.
I can't understand why changing service providers can't be like changing power companies. You don't have to notify losing provider of power company and billing stops at the losing one, when billing starts of the gaining one automatically.
I believe ISP's being able to put in contract one months leaving notice is a crock, and shouldn't be allowed, and at wholesale level the charges to ISP should stop at change over date from Chorous or whoever, so they're not out of pocket with customer they no longer have.