Genghis;
That's one of the reasons we have Vfe not Vf, and don't use Vg for the gear limits - structural engioneers already use f and g for negative g structural points.
Actually Vf is defined in 25.335(e) as the design flap speed. Vfe, the flap extended speed, is always less than or equal to Vf, as noted in 25.1511.