Oh wait, buck, you are under the misguided impression that Congress needs to sign off on the coin design. Ah, I see your confusion. Nope, not according to the text of the law.
31 USC § 5112 - Denominations, specifications, and design of coins | LII / Legal Information Institute
My emphasis for ease of reading.(k) The Secretary may mint and issue platinum bullion coins and proof platinum coins in accordance with such specifications, designs, varieties, quantities, denominations, and inscriptions as the Secretary, in the Secretary’s discretion, may prescribe from time to time.