The 610 faulting on NV condition codes is part of a journey of that bit of the instruction space from the original "really never executed, ie NOP" in the ARM1 (

The 610 faulting on NV condition codes is part of a journey of that bit of the instruction space from the original "really never executed, ie NOP" in the ARM1 (which just falls out of the implementation) through "this is unpredictable" (where UNDEF is a permitted implementation and helpful for flushing out stray applications relying on the old behaviour) until you get to the ARMv5 architecture, which uses the space for a collection of new instructions (which can't be conditional). A whole sixteenth of the encoding space turns out to be just too precious to waste.