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Companies that got burned by being IIB, esp Amex, will not touch him for a long time. There is no HP to be added as an AU, so he could try with a few & see what develops...
Being added as an AU will help his AAoA, his overall CL, & his payment history, provided, the account(s) he’s added to have low UTL, high CL(s) & perfect pay history. He probably won’t get that big of an overall score bump. YMMV.