"production and incorporation of X as Y 'have' or 'has' been widespread"? [closed]

This is somewhat complicated, actually. I'm inclined to use has here.

A question about a similar situation, -ing nouns and verb agreement, has unfortunately been closed. The answer to the supposed duplicate, My apples and orange are/is wrong?, tells us that subjects that consist of two noun phrases coordinated by "and" should have plural verb agreement.

However, my intuition is that in cases like this, "production and incorporation" is actually treated as a singular noun phrase. Perhaps the fact that both parts of "production and incorporation" are modified by "of the polymeric materials as modern materials in the civil engineering" is evidence for this, although I'm not sure.

I'll try to find more to back this up than just my intuition. For now, I've found:

• A question with a somewhat similar answer, Verb agreement in "Where is the Messiah and his Kingdom?"

• An example of "production and incorporation" being used with singular concord in a document accessed via Google Books. It might be incorrect, but at least this is proof that some people do this:

  Production and incorporation of new neurons during postnatal life has been evidenced in a series of nervous centers. ("Postnatal Neurogenesis and Neuronal Regeneration", by C. López-García and J. Nacher)

I also found many examples of "production and distribution has":

• Hybrid maize seed production and distribution has been left exclusively to commercial seed companies, which are owned by private individuals. ("Economic Analysis of quality protein maize (QPM) seed production at community level in Nigeria" by B. Ahmad, J.G. Akpoko, F.A. Showemimo and and N.C. Kuchinda)

• Thus, feature films remain an illustrative example of how production and distribution has changed and the impact of industry concentration. (Remaking Regional Economies: Power, labor, and firm strategies in the knowledge economy, by Susan Christopherson and Jennifer Clark)

• In the regions closest to central Sweden, systematic blade production and distribution has been detected in and around the mines of Świeciechów ("Blades as Messengers of Agriculture", by Helena Knutsson)

• Digital content production and distribution has radically changed our business models. ("SOFIA: Social Filtering for Robust Recommendations", by Matteo dell'Amico and Licia Capra)

• Theatrical film production and distribution has evolved into a multifaceted business (Entertainment Industry Economics: A Guide for Financial Analysis, Ninth Edition, by Harold L. Vogel)

This last one is particularly strong evidence because some editor seems to have consciously decided that the singular "has" is better than the plural "have" in this context: the Fifth Edition used "Theatrical film production and distribution have evolved into a multifaceted business."