Engines. Quite right. It is easy to date the instructions not to maintain airworthiness, as the evidence exists in (e.g.) reports from the Director of Flight Safety. But if or when they were implemented in individual projects teams is a different thing, as many simply ignored the orders, while others gladly obeyed. Much depended on the background of the project manager. In AMSO, the pressure was on from 1990, and by June 1993 any thought of a full audit trail was long forgotten. That was when the admin section in Military Aircraft Projects supporting HQMCs was closed. This was MoD's depository for many of the records necessary to demonstrate airworthiness - it was closed precisely because AMSO had chopped all funding and they no longer had any "customers" as the engineering staff had been told to get other jobs. (I left my post in August 1993). A matter of weeks later, the offices and storage facility were deserted and we could not access historical or even current records. (Little or nothing was on computers in 1993, and there was no e-mail). The staff were gone and there was no evidence they had even been tasked to archive the data. In turn, this led to your other point. There were no jobs, so no one was recruited or trained. In 1996, PE staff were thrown to the four winds, and when we moved to AbbeyWood I'd say about 90% of paper files were destroyed. On the Friday you'd sign over 10 filing cabinets to the contractors in London, and on Monday one would turn up in Bristol. It was completely random which one. The same year the Chief of Defence Procurement confirmed he no longer needed engineers managing engineering projects, so very few were left to train new entrants anyway. (And in any case, the new entrants skipped the previous 5 or 6 grades, so had no grounding and no concept of what their predecessors had been required to know. None even asked the question). By announcing this just after staff and their families had been posted to AbbeyWood, with half of MoD(PE) spending their time searching for houses, schools and the like (and, now, new jobs) very little attention was paid to the practical effects of his policy. Now and again it would be raised in Post Project Reviews, but it wasn't until Haddon-Cave noted the shortfalls that it received wider attention. Even then, he dated it to 1998, conveniently protecting those responsible.
While it would be a huge effort to reconstruct the glider audit trail, I believe it possible. The practical problem is MoD doesn't have sufficient expertise, and will be reluctant to issue a contract to those who do; to do so would be to admit incompetence and lack of corporate knowledge, which of course are components of airworthiness. I suspect a very small team of ancients are gradually picking through this, but wonder if the MAA are doing what they were advised to do in 2011 - submitting bids to resurrect the core, centralised functions. The evidence suggests not.