A lot of the dismissal is just something like "arrivalism". Like, the atom was harnessed in 1950, so it gets that date, never mind that reasonably safe designs took another 30 or 40 years. Computers existed, so never mind the massive cost decreases and capability increases that made them available and useful to many more people. Treat the arrival dates as the period society takes to integrate the technology and we are still in the transistors window.

(I think this is a reasonable point to make in the context where I started off talking about 50,000 years)