I've worked with engineering companies across Europe, and their documentation is always amazing, with full traceability of every component going back to the 80's. Everything from processes to weld inspections.
I'd assume that a company engineering weapons would be the same.
Otherwise, you're in the business of archeology, a field which itself requires extra-archaeological context to make sense of its own findings.
I'd expect the same standard for anything military/involving national security, alone for the fact that should war come, there will be a need to rapidly expand production, to rope in everyone able and willing - and that won't work without complete documentation.
I presume there are good reasons why this and exactly this is happening (and probably not only at this manufacturer), if for nothing else than reducing costs... not maintaining something is always cheaper than maintaining it.
In a sense you could consider each person who has knowledge to be an air gapped data bank with a limited lifespan. Theres some very clear issues with that system, but that's arguably the effective intention behind not documenting war related development until well after the useful lifespan of the development.
But that's probably where the issue lies. Those plans make certain assumptions based on the technology, tooling, and processes in use at the time. The bill of materials may reference off-the-shelf parts that were readily available back in the 70s and 80s but are now considered obsolete. Some of the raw materials specified may no longer in use due to new environmental regulations, changes in industry standards, limited availability nowadays for any number of reasons, etc. Machining processes may be documented in the context of machines, tools, and procedures common a the time that we simply no longer use. Similar challenges exist for every part of the process, from sourcing materials to quality control.
You can document everything with a great deal of detail at the time--likely the case here, by the nature of manufacturing complex products--but that doesn't mean it will be understood in exactly the same manner forty years later. No engineer can predict how processes and standards will change over that kind of time frame; the best they can do is document everything clearly enough that future engineers can work through what's left behind and adapt it as needed in the future.
Bringing in retirees likely expedites that process. They can almost certainly work through it, but if a few phone calls and meetings with retired staff can speed things along, there's no reason not to. It doesn't mean someone screwed the pooch in the past. In a military context, existing stockpiles are meant to give you sufficient time to restart production.
With a computer backup, you can monitor that the system is functioning and verify the recovery process. You can even confirm it directly, restoring backups to a separate system. You can't do that with a manufacturing line that hasn't manufactured anything in forty years. Either you keep it active, manufacturing items you neither need nor want, or you try to constantly update your plans every few years on the off-chance that you'll want to build more outdated Stingers in the future.
That would absurdly wasteful, and even if you catch some changes in procedure/systems/materials, you'll miss plenty of others unless you actually try to restart production. No matter what you do, there's going to have to be a certain degree of interpretation work that's needed.
Europe isn't overflowing with gigantic tech companies nor defense contractors that would have what you're describing going back to the 1980s and 1990s. You can likely count them on one hand, given how few there are to begin with.
There's a very big difference between knowing how something was made decades ago via schematic & component lists, and having to restart very high-quality production from scratch, including the ancient components. Building things related to technology during their actual time + place, is considerably easier than trying to recreate that time + place decades into the future and at scale.
That is completely delusional.
>You can likely count them on one hand, given how few there are to begin with.
Giant (or just large) Technology/Defense companies, a random sample:
Siemens,Bosch,Phillips,Renaut,Airbus,VW,Thales,Thyssen Krupp,Rheinmetall,Saab,Dassault,Zeiss,ASML,NXP,BMW,Mercedes,Liebherr,MBDA,...