Look, there's a basic problem here with Dr. Bill's proposal--credentials are an imperfect, AT BEST, substitute for skills.
And it is SKILLS not credentials that are the issue in diving.
Let's say you've just popped off the plane in Vanuatu all hot to dive the Coolidge. Dive operator gives you two choices for your buddy:
A) Sammy McWet, fresh off of his OW and AOW courses on the GBR only five days ago! Sammy has made a grand total of 17 dives, but since he is AOW is "certified" to make "deep dives. In fact, he is good to go for a year!
B) Ruth D'Crustee, 350 logged dives including regular and significant experience at 40m and below in current and trecherous conditions. Never took her advanced course, however, so she's still only an OWD. Alas, however, Ruth had a child three years ago and hasn't dived in the intervening years.
So, who are you going to choose as your buddy? The "certified expert" or the REAL expert?
Are you safer diving with Ruth on the Coolidge on the second dive day (after one day of easier diving for her to get her scuba legs back) or with Sammy with his "certification?" Would you insist that Ruth redo her entire OW course to dive with you?
Please, let's be realistic here.