A Broker of Record letter (BOR) is a document signed and dated by the insured which grants a specific broker the sole right of representing the insured to insurance companies for the purpose of placing coverage.
Two different brokers can’t work with an underwriter on the same account at the same time. There can only be one Broker of Record.
It’s important to note that BOR’s are specific to coverages so you can have one broker work on D&O and another work on E&O (though this is highly discouraged for many reasons) and that the BOR can be rescinded by the insured at any time. It isn’t a binding agreement.
Most carriers, upon receiving a new BOR letter, will give the current broker a window of 5-10 days during which they will not work with the new broker, giving the old one an opportunity to win the business back. This window can, and should, be waived by the old broker if the insured requests it