The technique to making true Damascus steel was lost in the mid 1800s. The technique and composition to Greek Fire was lost in the 13th century or 19th, depending on whose stories you want to believe.

We were well on our way to losing the schematics and information on our original Apollo and Gemini space programs until they started trying to sort and salvage that data a few years ago. The problem is that when we replace something old with a better technology or limit the knowledge of a technique to a few people, we rapidly lose the methodology of 'how' to do the technique.

In the case of proper war and hunting archery, when guns became more common and easier to use, people gravitated to them because they were MUCH easier to learn than archery. Archery required specific training for war and for survival it was from the time you could hold a bow. Anyone could learn to use a gun quickly, so people just....forgot how to properly use bows. Probably as soon as the remaining archers died out.

It needs to be placed at 9 Vincent Square in the football field and loaded with Greek fire boulders with a trajectory dialed-in for Buckingham Palace for a November 5th celebration not soon forgotten...