I used to work for a large military supplier as a QA engineer. One of our products was an intervalometer for aircraft-borne rocket launchers.
The PCB for that thing was chock-full of shorts, connection bridges, extra resistors and caps tacked on as if they were aftertoughts - and the whole affair was then potted to avoid failure due to vibrations.
When I enquired about that sorry mess, and asked why we didn’t redesign the board entirely (which was my job after all), the reply was: as long as we modify the original board from the 60s, it’s a modification. If we redesign the board, it’s a new product and it’ll have to be certified by the FAA and the EASA as such - by modern certification standards. The 1960s board was never certified because it was a military product, and it was exempt back then, so we could do anything we wanted.
Yikes… The damn thing was more tacked-on modifications than original product. And I know for a fact that it’s still flying…