The last of the good Portriga was manufactured in the late 80's. The emulsion was changed by removing the Cadmium so as to be more environmentally friendly. This effectively destroyed the best properties of Portriga Rapid.
Because it is a Chloro-Bromide emulsion it does keep somewhat better than pure Bromide emulsions.
It really depends on the packaging, I have a nice supply of early 80s Portriga which I have kept refrigerated without any ill effects.
If the Grade label is dark blue, or even light blue with no red markings in the label and it is not fogged it is worth its weight in gold.