auv-ee
Once a design is certified, they probably follow the principle: "if it's not broken, don't fix it."
"If you can still get the famn dool parts."
(I'm enough of an antique that I know from hard experience this is a pesky detail. I wonder if anybody could build the GPS frequency synthesizer and distribution unit today to the schematics generated from my design back in the mid 70s. It used already completely obsolate TTL parts because they were rad hard and the newer parts were not hard enough.)
{^_-}