SQ won’t open up the last minute space.
Or else many ppl will be booking cash fares and cancel at last minute. (Cancellation fee only S$130).

You can try at airport for paid upgrade or miles upgrade (advantage) but chance is that the suites are usually full. Or SQ does not even open up the miles upgrade option.

two flights are A380 but the 322/317 pairs awards are only available to PPS.
so you left with one option (308/319 pair).