I had a thought. writing seems like one of the middle tiertechs a society should get as there are many techs before it that'd be needed. Stuff like dye making, oral history, story telling, counting, etc.
also, I'd like to see the techs needing the material in question to experiment with in the early stages but as you get more and more into a more advanced society to start to allow predictions and theoretical tech to be attempted. This of course would tie into having thousands of techs. And the theoretical tech could fail if they don't have the necessary knowledge of other techs and maybe even consider it a dead-end and not bother researching it again until someone with the necessary tech makes the connections. Further more there could be techs that just appear to be useless curiosities that much later prove to be extremely important base techs for other technologies.