On the first blocks mined, there were some input script on coinbase transaction (which is useless as it is not used at all in bitcoin's protocol). In this script, they were only 2 pushes in stack of 2 VLI: one for a timestamp (not sure), and another by an extranonce value. This value was used to alter the coinbase TX hash, thus the merkleroot hash, then the block hash value. I guess it was another variable which could be used to reach a valid block hash value (additional ot nonce & timestamp or re-ordering transactions).

This value is not existing anymore and recent blocks have a empty input script for coinbase transaction.