You've heard of ESRs? Nothing is specified on a commercial project without an ESR. That covers everything you're asking about.There are several questions. Is the methodology used by the manufacturer appropriate? Do you trust the manufacturer? What do you feel is appropriate? What can be legally compelled?
Building departments are concerned with the question of what can be compelled. The other questions are the providence of the code writers, the applicant, and the design professional on the project.
I just want to weigh in with a thumbs up for use of the term "engineery". gonna have to borrow that oneThe 12" is the punch shear dim. Assume a 45 deg shear plane through the slab (footing) from the edge of the column. So a 4" square column would have a 12" square effective bearing area. That assumes no reinforcment. It gets much more engineery once you start adding reinforcement and your footing becomes a bending plate with spring supports.
I would be ok with a 1500# point load on a 4" slab by inspection.