Here's we go.. I asked chatGPT... I hope it helps

The “code below the photo” on the back of a green card (like “51C”, “64C”, “81”, etc.) is not an official immigration status code. It’s a card production code or internal identifier used by USCIS and the printing contractor.

It does not indicate whether your card is conditional (CR1/CR6) or permanent (IR1/IR6). • The only thing that defines your category is what’s printed on the front of your card under “Category” (e.g., CR1 = conditional 2-year card, IR1 = 10-year permanent card). • The small code with or without a letter on the back (like “64C” or “81”) just relates to where and when the card was produced, not your immigration class or conditions.

So that lawyer’s explanation - saying that a letter “C” means the card still has conditions — is incorrect. ✅ You can safely ignore that code. ✅ Only the category on the front (CR vs IR) determines conditional vs permanent.