Did you look in the electrical assembly manual and shop manual, including the schematics where the basic part numbers are often identified? I don't have 1969 versions so can't do that. Also I don't have a 1969 parts catalog (one year only) to check - do you have that?
Most of the Ford documentations available outside of the engineering environment pertain to vehicle service. The fourth character of the C9ZA prefix, "A", represents the group responsible for the design. The fourth character of the D1ZZ prefix, "Z", represents a service part number. I'm seeing what you found, and at least according to the 1975 Ford and L-M versions of the 1965-1972 Master Parts Catalog, there was no 1969 Mustang "air conditioner blower motor feed wiring assembly" serviced; no C9ZZ part, and the D1ZZ application is for 71 & 72, and does not cover previous model years.
In the grand scheme of things, if you consider volume, the need for front and rear bumpers due to accidents, compared to the need for this part, is a million to one. This wire assembly is simple enough that, if there is a problem, it could have been repaired...improvised.
Lastly, I did see the following 19949 service (Z) parts in the 1977 version of the OSI. Alas there is no C9ZZ part listed, only a 69 Bronco (C9UZ) part. The fact that even the 1976 D6DZ part was NR (not replaced) in 1977 kind of confirms that these parts were not high volume.