It looks like silk top hats were still being made in the 60s so presumably it might still be possible to find people that worked in the factory and recover the knowledge if people really cared.
Possibly but the 60s is a very long time ago now… My parents were both adept in Fortran in the 60s when they were in their twenties but now in their mid-eighties I doubt they would be much good at helping someone who wanted to problem solve anything using Fortran!
But restoring knowledge is against value extracymtivism so not worth it at all.