hardened exhaust seats

From what I have read, hardened seats started in 73. I think all cars were burning unleaded by 75(by law) and so manufacturers started getting ready early.
Will a good valve job make a difference? No. Many people argue about whether hardened valve seats are even needed. I have never personally had a problem with sunken valve seats nor have I ever even seen them myself. Only plenty of stories of them. Enough that I would tend to believe them. Dennis