I emailed this to a Square D rep about 2 wires under one clamp on QO breakers.

Youare correct the QO 15 thru 30amps are UL'ed to
accept 2 conductors per the 0730CT9801 you
refferenced.

Thank you for your Square D inquiry


Schneider Electric/Square D Company
Jim Betournay
Product Support Specialist
Customer Information Center
1-888-778-2733

He has been most helpful.
P.S. does anyone else receive the Teamworks news email from Square D?