You are confusing Institutional diapers with medical diapers. Institutional diapers are those sold to Nursing Homes, Hospitals, and other long term care businesses. Medical diapers are designed and sold to the public for incontinence. ABDL diapers designed for the ABDL market. Until Bambino came around there were no ABDL diapers, and The Bottom Half Group sold a plain white diaper identical to the Bambino, except for decoration, as a medical diaper.
MegaMax may blur the line between ABDL and Medical Diapers, it was designed for a medical purpose first. Whereas Little for Big, Rearz, Tykables, ABU, and others were designed for the ABDL market.
Perhaps a better term would be Incontinence Diapers, as opposed to ABDL Diapers. But the ones used in hospitals and nursing homes are Institutional Diapers.
So MegaMax is an A grade Medical diaper, NorthShore Supreme would be B grade. Abena C grade, Tranquility D grade, and Depends F. Attends are Institutional F grade, at least the ones I got.