Hi John,
I agree with you,
Condition Code is changed by some machine intersections,therefore
the result of perform ... or c-c = 0 is an invalid and ambiguous
code.

This is documented in chapter 10 or 11 of the COBOL manual.
for example :
 if c-c = 0 then
    do this
 end-if
 if c-c <> 0 then
    something else
 endif

Is incorrect , since the first end-if might change the c-c.

Michael