Often at big companies the staff turnover is such that there's a kind of "institutional memory loss" because there's no one there that was working there 10 years previously, let alone 20 to untangle the complicated provenance of the mixes and say 'well actually, the three bonus 5.1 mixes on the 2012 DVD-V come from the 2003 UK SACD, and those were sourced from the 2001 US DVD-A.'
Great point. I've been in my industry for decades [tech], I've always heard old timers wisdom referred to as "tribal knowledge."