I once encountered with this issue of DCB at New Delhi airport. Add on card of dcb was swiped first then primary card. Add on card did not work. However when primary card was swiped first then add on card , in this case both worked. I guess in 1st occasion, both were swiped simultaneously in two...
Master and visa has done agreement with most of the airport lounges however card issuing bank restrict this benefit to their product . So it depends on bank to pass lounge access as complimentary to their cards. The list banks keeps revising every year.
Hope it makes clear.