Word of caution... if you book as round trip as IND-ATL-SIN-IND but skip the first IND-ATL segment because you're already in ATL, it may cause problems with the rest of the ticket since they'd think you were a no-show, or end up having it repriced at some crazy rate.

Would be better to have it done as multicity ATL-SIN-IND since it should be almost the same price.

Bummer about the O inventory going away for the ATL-NRT segment... unfortunately if O becomes available it doesn't usually last long for that route.