The customer, Owner, person holding the gold, whatever, makes the rules. They can reference any acceptance criteria they feel meets their needs. As long as the requirements are spelled out in the contract documents, all is fair.
This practice is not uncommon. For example: I have a client that designs and manufactures components in accordance with ASME Section I. The material, stainless tubing with a wall thickness of 0.035 inch, is thinner than the undercut allowed by Section I. We modify the visual acceptance criteria and limit the undercut to 10% of the wall thickness.
Best regards - Al