For the simple reason that it is "slang" and the real title of the document is Ford Car Parts.
Jim
With all due respect and appreciation, which is not insignificant...
Smack dab on the cover of the 1975 dated publication Form FP 7635-A, and on the General Information page 1 are the terms "Car Parts
Master Catalog" and "Ford Car Parts /
Master Parts and Accessories Catalog" respectively.
The term "Master" is used in the 1949-1959, 1960-1968, 1965-1972, and 1973-1979 multiple year catalogs, and conversely the term "Master" is not used in any of the "single year" or 2-3 model year combination publications.
My conclusion is that the word "Master" is a key term when referencing the publications that spanned 7 to 11 model years, and that MPC is a reasonable abbreviated acronym. Slang perhaps, but infamous - I think not. To exclude the term "Master" when referencing the publications that Ford classified as "Master" would be an error of omission.
My $0.02 cents as some would incorrectly say.
John