Individual Airpod Pro earbuds serial number not working, but the charging case comes back as a valid apple device

Im attempting to meet some one to purchase some Airpod Pros first generation ear buds. Like i said in the title the charging case serial number located on the underside of the top of the charging case came back as a valid apple device on apples serial id website. However when i entered the serial number located on the individual buds into the same website they came back as invalid. I attempted the same with another pair of Airpod Pros that i know are real, and again they also came back as invalid. So do the individual earbuds serial numbers not register, or are the earbuds fake??