What is the difference between ASME B16 and MSS SP 44?

ASME B16.47 Series A (MSS SP-44) Flanges Notes – ASME B16.47 Series A flanges (> NPS 26) are MMS SP-44 flanges. MSS SP-44 also covers NPS 12 to NPS 24 flanges which are equivalent to ASME B16.5.