Well perhaps GM thought of those as non-standard models because they do have the Z28, Z22, but no Z10 or Z11 and they also don't list the COPO #'s......although they do have some stranger COPO items listed like for 69: ZV7: COPO Transmission M21 or ZP1 C.O.P.O Tires but no 9511, 9560, etc.
Strange......
Paul