Hello GS

In plain, language it means that specifying these bolts, the engineer must check that the flange will not leak in service. The SA-193 B7M bolt is weaker than the B7 bolt.

The calculation in accordance with (say) ASME Section VIII, Division 1 does is not provide a guarantee against leakage. In fact, there is no known procedure (to the best of my knowledge) that provides a guarantee against leakage.

It is worthwhile to read Appendix S of ASME.