STH
Very slow and cumbersome in the extreme.
As I said earlier, very often this slowing down is a political decision to delay expenditure. Otherwise, you are spot on. One of the practical problems is the URD is often physically impossible to attain (never mind sustain) and after some years fannying about the project manager is forced to issue a clarification paper telling London (a) what is possible, (b) what is affordable within the endorsed funding, and (c) what they'll get. A solution emerges.
M2N
If you own the overall product then you need an in-house organisation to track obsolescence and manage the impacts
Unsurprisingly, mandated policy until the department responsible for management and oversight was disbanded without replacement in June 1993. In July 1996, two generations later in posting terms, EFA (Typhoon) convened an urgent meeting at which one of their very expensive consultants declared that they had uncovered a phenomenon called electronic component obsolescence, and would wish to open dialogue with attendees in an effort to work out how to deal with it. We gave him the mandated Def Stan and left. It doesn't take long for corporate knowledge to disappear.
this does not come cheap.
Which is why MoD stopped doing it! But this ignored the fact that the consequential cost was measured in lost aircraft and lives. The same solution emerges.....