50,000-60,000 years ago there could have been another 2,000-6,000 period of near linear technological progression and trade and you would never know.
The conditions for fossilization are extremely rare. All we have is that people got there and then a hairdresser got fossilized in a mudslide and we are now elevating this person as a representative of their whole species.
plastics aren't a natural progression. it is just as likely that the social and survival pressures were very different, and that the innovations were very different
and its just as likely that people merely got lucky with primitive rafts and canoes for long distance travel
The conditions for fossilization are extremely rare. All we have is that people got there and then a hairdresser got fossilized in a mudslide and we are now elevating this person as a representative of their whole species.