How to Link Tables in a Complex Many-to-Many Relationship?

np,

This sounds like a vanilla situation.

You already have a table of physicians.

Make a new Table of Credential Masters.

Then make a table for Physician Credentials as the Join table.

Make a relationship where 1 Physician has many Physician Credentials and look up the Physician name  and go to the field for Related Physician and set the Physician Name as the Proxy.

Make a relationship where 1 Credential Master has many Physician Credentials and look up the Credential name and go to the field for Related Credential Master and set the Credential Name as the Proxy.

Then add fields on the Physicians Credentials table for your various approval and expiry dates and any comments.

I think you biggest issue will be to un-clutter your app with what you have built to date.