4 1/2 or 5 quarts of oil with 1/2 quart of ZZDP?

ASTM, API, SAE, and the like are technical organizations that set up specifications for essentially everything in life. Fuels, Lubricants, cement, plastics, electrical products, you name it. They are there for a reason. To give the consumer exactly what they want and/or need for things to function. But they do favor the large producers that can afford to run tests to meet the specifications and register the products. Small producers, e.g., specialty oil blenders, can't or don't want to meet these requirements. Actually, API eliminated the older engine oil requirements to keep those high ZnDTP products off the market to prevent misuse in modern engines. Much to the distress of people owning older engines.
So much of this is driving by Fuel Economy and every tightening emission standards.