EPA regulations are written by lawyers, not scientists and engineers. You wouldn't believe the number of test procedure and self contradictory laws they write and we find every day. By self contradictory I mean, one section of law says X is not legal. Another section will say X is the desired policy of EPA and will subsidize it with a $2000 per engine program.
The corporations will lobby for regulation that supports thier best interest. For example, regulatory alignment with all the other world agencies to make compliance easier/realistic, or regulate the B and not A, or make it difficult for start-ups to compete by requiring difficult and expensive facility certification and testing.
Then the EPA lawyers write these laws while working with the environmental groups with the goal of being sued. The EPA wants to be sued, because then a federal judge will tell the EPA "you must regulate Y in this harsh way" in the courts decision.
That is how the EPA regulatory sausage gets made. It is the most messed up thing you would never believe.
Honestly, I would rather deal with the ATF, FBI, SS, or IRS any day of the week than the EPA. With the others I have some defined rights and due process procedures. The EPA is above all due process and rights.