some people may consider bambay bl gr to be a subtype of O-...........they are right in their logic as the abo system is based on A & B antigens only and not the h antigen
The important distinction comes in blood transfusion

O- pts do not have anti h antibodies in their blood while bombay bl gr does

so bombay pts can be transfused only with bombay blood..........but they can donate blood to O- pts

(during transfusion cross matching between donors cells and recipients plasma)

people with O group as well as well as a,b,ab group have h antigen of their RBC.

Ha ha .... I suppose something for all to keep in mind when practising in India.