Checking luggage can often create challenges (or cause unwanted attention) on some point beyond planning, so think them through. For instance, if you skip Colombo-BOM, be prepared to explain why you want to check luggage in BOM for BOM-JFK. Likewise, if your return is JFK-BOM-Colombo, be prepared to explain why you want you checked luggage in BOM. A 21 hour layover might be a good excuse.

Not using the last leg of a returning ticket from a U.S. gateway city to another U.S. city is easy because the airline has to produce your checked luggage at the gateway city for customs inspection.