This is a very thought provoking idea. Ise Jingu is the practice of rebuilding a set of famous 7th century shrines exactly every 20 years, using traditional techniques and materials, to preserve process knowledge.
These examples are of process knowledge with tangible outputs. Can we recognize less-tangible examples?
I'm eyeing a bunch of societal and well-being-related trends but it's hard to disambiguate between knowledge decay and obsolescence due to changes in context.