Since the AHJ can accept alternate methods and materials, this simply becomes an issue that does not comply with the NEC. I also have installed an attachment plug in this manner for years, because it was an accepted practice. U.L. lists an attachment plug just for termination directly to branch circuit conductors. It is just extremely difficult to discern these for those that are required to be terminated on Article 400 cords and cables. To say this is not appropriate is, to say the least, a "non-statement."