I would take that to mean Appendix A (certain standardized sizes and designs in the 6th Ed), Appendix D (higher-strength design, now the default method in the body of API-650) and Appendix B (foundation design).
Usually, "App" is part of the nameplate text, there's a box, and the "ABC" whatever is stamped in the box, all that apply.
It looks like those Appendices have changed applications some through the years, so the current ones don't correspond to the 6th Edition ones.
And in the current standard, they're "Annexes", but in all the older standards they were "Appendices".
Do you know where I could find a copy of 6th Edition Appendix D? API doesn't have it (believe it or not), IHS doesn't have it, and Techstreet doesn't have it.
I believe ADP stand for alternate design basis (which was Appendix D in my old 3rd edition...I think) which allows the use of higher strength materials (thinner) usually with more shell stiffening and higher design stresses are allowed.