I realize this doesn't help but there's an old story about dmr being asked in the early or mid 80's to look at a clone which he checked for specific bugs he was aware of (but apparently no one else was). It turned out to be clean. I don't remember the details but that might be a good starting point?

Apologies to Andrew who gets this mail twice (in his in his private mailbox, and on the list). I assumed gmail would send it to the list as I intended but it didn't, so I had to resend. Sorry!

On Sun, May 1, 2022 at 1:34 AM Andrew Warkentin <andreww591@gmail.com> wrote:

What was the first "clone" functional Unix (i.e. an OS not derived
from genetic Unix code but highly compatible with genetic Unix)? Idris
is the earliest such OS of which I am aware (at least AFAIK it's not a
genetic Unix), but was it actually the first? Similarly, which was the
first "outer Unix-like" system (i.e. one with strong Unix influence
but significantly incompatible with functional Unix)? Off the top of
my head the earliest such system I can think of is Thoth (which
predates Idris by almost 2 years), but again I'm not sure if it was
actually the first.