Hi, Mark. Typically, items that are test issues or very, very rare such as your SI promo card are not required but optional if a collector adds them. I have done that with a number of cards (requested they be added but come back as optional). I have the 67 and 68 Discs, for example, and they are optional. Same with Proofs. PSA is not always consistent. The 1972 Test Disc is part of the set. I may have added it. The 3D 68 and Dice Game are optional. I often think it is very random. I have a few items that I believe are one of a kind that are part of the set, so not sure what the process truly is. I doubt I answered your question because I am not totally sure there is a clear answer.
I have a lot of cards I would be happy to trade with you that might help if interested. I am constantly looking to upgrade. I would love to see a pic of your SI Card.
My email if you want to chat more or swap cards you are missing or would like to upgrade:
Charles.strite@yahoo.com
Look forward to chatting more.
Charlie