Q: If so if you were to to have a C13 with a #11 would that be C13(#11) or D/Cmaj7?
A: by the way, C13 uses Bb, not B. when maj/min is not specified it means dominant which means flat 7. C7 has a flat 7, not natural 7. for natural 7 you would need to say Cmaj7. again that's just my experience from being in the biz