Rescue is not a specialty.Wow! I know you have a Nitrox card and a Rescue card somewhere in that stack. You never took 3 other recreational specialty courses?
4 specialties (max of one non-diving, like Nitrox) plus Rescue, and 50 dives is all it takes for SDI Master Scuba Diver.
I have a drysuit specialty card and an equipment specialist card. I think that's it for PADI specialties. I have specialties from UTD and PSAI. (People seem to think PADI is the only agency that teaches specialty classes.) I am a technical diver, and when you go through technical diving, you need to get a card almost every time you do a dive (yes, I exaggerate). I have loads of instructor cards telling what courses and specialties I am entitled to teach.