not as fake as you are
lost the blueprints to the machineray… yes
lost the tech… no
the only "lost" bit I know of is the art of casting rocket engines and that was only temporary
that was lost because we stopped making them in the 1970's and the artisans who knew the craft retired or died of old age
new designs have been created and the engines have been successfully fabricated and now fly into space with engines cast by new companies