Nice piece DBP.
"...engineering judgment to use outdated CA instructions over current regs..."
All aircraft, from the Wright's Flyer to today's F-35, have been built to "a specification".
Even today all aircraft are mainly held to their original specification (as that's the designed they were built to meet) and operators and authorities are supposed to have access to that spec when accepting new and second-hand aircraft - to compare it against its designed origins and current modified status.
Used aircraft are 'normally' assessed against their original spec or changed design spec. In former days New regulations were not normally used to assess an old aircraft and are not 'normally' retrospectively applied except for new modifications. The aircraft should meet its original or (certified) modified specifications.
Some aircraft have been modified to conduct new roles (Sentry, Sentinel, Shadow, Voyager etc.) and have developed new profiles and parameters in which they operate. (I'm not sure about Sentry here, but that not my point)
NORMALLY, development of changes such as those would be through defined and legal practices in design and production followed by thorough testing and retesting to confirm, define or rectify performance limitations.
"What if", years ago, some military/contractor establishments did not conduct said practices and just bolted/soldered some stuff together - that happened to work - and just left it at that? ...And then happened to sell some of that stuff years later?
How could anyone justify "using engineering judgement" without any supporting documentation or evidence?
(I am not saying that anyone has done this - it's just "What if?")