I like your logic, but I am skeptical that it will be of use in this case. In my time machine, the accepted notion of time can be warped and it does not necessarily correlate to stock prices. My ultimate determination of when we have arrived in 1974 will be when stock prices have reached the bargain levels last seen in 1974.
I am thinking of trying to start a project to exhume Richard Nixon and Spiro Agnew and have them brought back to life so that they can ring the opening bell at the NYSE in order that everyone could know just where we are in the stock-time continuum. We could tell the doubting public that Dick and Spiro never really died, they were just hibernating with the polar bear.
Elvis may also still be alive and he may come back into the building.