The important thing is that reserves only extend 20 years ahead of time. There is no incentive to spend money now to find oil that you will need 21 years in the future. There is an incentive to spend money to find oil that you will need 10 years from now.
That is why for the last 80 years we have between 10 and 20 years of proven oil reserves, and will probably have 10 to 20 years of reserves for the next 80 years.
Coal can be hydrogenated to produce oil, but that doesn't count towards oil reserves.
This information is not correct. In 1980 the world's oil reserves were 28 years of the consumption at the time. In 1985 it was 32 years. In 1990 it was 41 years. And it has stayed between 36 and 42 years since then.