See 210.4 Multiwire Branch Circuits
The requirement is for:
"(B) Disconnecting Means. Each multiwire branch circuit
shall be provided with a means that will simultaneously
disconnect all ungrounded conductors at the point where
the branch circuit originates."
That seems to allow the use of listed handle ties as well.
And (D) "Exception: The requirement for grouping shall not apply if the circuit enters from a cable or raceway unique to the circuit that makes the grouping obvious"
