1. For the knobs, the assembly manual calls for (2) C7ZA-18817-A whereas the MPCs (multiple versions) don't call out any C7ZA or C7ZZ variant. The 18817 basic part number stamped on the part, and listed in the assembly manual is identical to the MPC.
C7ZA-18817-A is the knob's actual number (sometimes called the "engineering part number) of the part. The service STOCK number, the number printed in Ford Car Parts (aka MPC) for replacement, the number on the box, the number on the dealer's shelf, the number to replace the knob is C7GY-18817-A (a Comet designed, Mercury dealers service part).
To replace the one you got from the dealer's shelf, the service department would order C7GY-18814-A and eventually, a cross reference document, deep in the Ford service part system would say to use the document to make a C7ZA-188147-A, or it's Comet equivalent. Motorcraft uses a "locator code" on their boxes, that is a shortcut identification system.
It's the system that works. You can see a similar system at Home Depot, the Home Depot SKU (Stock Keeping Unit) number on the shelf label (the one with the name and price) for the part, and the 12 digit bar code on the box. There may even be a model number in there too.
Jim