UC Reward seat availability VS2 EWR LHR

Hi all,
This is my first post but I'm a long term lurker! My partner and I are off to NY in May, originally we booked Econ and then upgraded to PE with miles, I have enough miles left to upgrade us both to UC which I managed to do yesterday on the outbound VS1 8th May which is midweek, however currently there's no availability for the return VS2 on 12th May. I appreciate it's an impossible science(!) but in your experience is the VS2 on a Sunday likely to become available or is that a popular flight? The lady I booked with advised seats are often held until a few weeks before which has been true of the outbound VS1 bit sadly not VS2!
Any thoughts much appreciated
This is my first post but I'm a long term lurker! My partner and I are off to NY in May, originally we booked Econ and then upgraded to PE with miles, I have enough miles left to upgrade us both to UC which I managed to do yesterday on the outbound VS1 8th May which is midweek, however currently there's no availability for the return VS2 on 12th May. I appreciate it's an impossible science(!) but in your experience is the VS2 on a Sunday likely to become available or is that a popular flight? The lady I booked with advised seats are often held until a few weeks before which has been true of the outbound VS1 bit sadly not VS2!
Any thoughts much appreciated
