[Blood Legend]

I seem to vaguely remember Rome having a sudden TL jump by studying old ruins. One of those ninja turtle artists had a hard time convincing workers that his florentine domes would stay up until he went up there and started building it himself.

I think its entirely plausible there's an armor renaissance going on. Some armorers are set in their ways, others dont have the equipment, information or both, but a great many simply don't believe the new techniques are real. Any examples shown must be parlor tricks. "Sure its stronger but it must have taken months to make a piece that can beat my brigandeen! Youre just trying to steal my customers!"

Further still, the new armors attract emboldened brigands who've heard ill rumors, thinking they'll pierce through like paper. So customers shy from its lethal attention grabbing characteristics. This rumor isnt self correcting because those same brigands usually die pretty hard.