You are also seat locked unless you went up in pay. If, after two years, you move laterally 737->320 then you would be locked on the 320 for two years. A 777 CA that bids 737 FO would be a seat locked 737 FO for 2 years. He could not immediately bid upward, but once his seat lock expired he could become an upward bidding seat tourist. This is my understanding of the contract anyway.