Good to have the weight on this one, but I'm also skeptical that there is a missing clad layer. Surface discoloration seems much more likely to me, but I'm interested to see where we net out on this one. @mack, this site might be helpful as you continue your research:
https://www.error-ref.com/?s=missing+clad
"If you climb a good tree, you get a push."
-----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed."
-----King Adz