Originally Posted by stargold

The option to pay for Premium Y at check-in is likely to be the fare difference between a Y booking class ticket (which allows you to sit in PY) and your fare paid - i.e. a lot of money. I haven't yet heard of just a fixed price upgrade to PY on the day of departure.

On NH, only full Y booking class can pre-reserve seats in the PY section. NH elites (not the *S level) can sit in the PY section if space available on the day. Other Star Golds may be operationally upgraded, but if ordinary Y is not full then you will not be given a PY seat.