I have seen mention of the deep password linkages from multiple sources, but from personal experience I believe that it is of relatively recent origin — like High Sierra recent. <snip>
Based on my past experiences, that sounds reasonable.
As far as a KB article on the subject goes since Google, DuckDuckGo,
et. al. can't find anything, I think you are going to have to dig into Apple's
Develpoper's Documentation probably under
Security.
NOTE: the Developer's Documentation assumes a working knowledge of Objective-C and Unix so be forewarned.
I, too, have had no luck searching (other than finding others with the same issue), and as for Developer Documentation, I've looked at some in the past, and it's left my head spinning. (I once asked my buddy C3PO to look at some Objective-C, and he responded "It's Fortran to me."
)
I think it's about time to lean on Apple; this issue is 7 months and 5 versions of macOS old at this point, and it's long past time for them to have at least examined it.