I don't think spares shortages are particularly to do with problems being 'hidden'. Any ADFs due to spares shortages should (!) have an associated demand placed... At least any I signed did, admittedly in the knowledge that some bits might not turn up for six months or more. Spares shortages are as old as the hills, and could obviously be solved by stocking shed loads of everything at every site. But that's expensive, so we do it less and less. Increasingly, availability or capability gets compromised as a result... But not convinced I ever saw spares shortages directly affect airworthiness. It might have cost lives because we didn't have a frame for the task when no amount of bodge tape would put Humpty together again and enable a safe ADF or Lim, but that's a different argument.