its rather simple

there is no space for a colored coin in the registry so its rather easy to collect a full set without having these coins in there. the reason these cant be graded is because they were post mint which means they were colored after they left the mint or plated after they left the mint, and no respectable grading company will grade any coin that has been messed with like that after the coin has left the mint. Hope that helps you to understand why they cant be graded and why they just arent considered "registry quality" coins no matter how good they look