I inherited stock in 1980 and sold in 2023. Broker provided 1099B but only provided basis from 2012 on.

On the brokers 1099B they list all transactions except for the cost basis for the original shares which i inherited in 1980. Turbotax is telling me i need to upload or mail in a 1099B because i need to come up with my own basis for original shares? The broker already sent in the 1099B to IRS, why do I?