Joe C did a pretty good job with the X codes. I'll explain a different way.
Brian said that X66 is a style trim option and then describes it. The description is correct (black body sill and tailpan, 1/4 gilles), but it for a BB with the absense of a style trim option.
A X22 body is a BB with Z21 style trim on it and adds driprail and wheelwell moldings.
I thought X22 included both bright taillight and headlight trim. I need to check on that.
See
http://www.camaros.org/numbers.shtml#XnnCodes for all the X code details.
The COPO's were very defined (remember other dealers used the same #). Yenko could not modify them each time he ordered the cars. The difference could be how the plant interpreted the order.
No known COPO's came out of the LA plant.
Kurt