Originally Posted by
lamphs
This was a couple of years ago for me (2019). I wanted SIN-NYC (forgot if it was JFK or EWR)-WAS (any Washington DC area airport). Space was available for both segments (on the SQ website), but the only way I was going to get NYC-WAS was a separate booking AND SQ could not combine/link PNRs. The miles required for the NYC-WAS segment was quite high as I recall and I just ended up booking with UA directly.
This is the issue I raised above. It's most likely that your SIN-NYC flight was not available as a *A award but was rather only available to SQ Krisflyer members. In order to have all segments as one award, all the segments must be available as a *A award.