According to the back of the card, the code doesn't expire till May.
If you can find someone with a spare code, you should be good.
I don't know if it'll work, but try contacting Nintendo support, they still might have codes.
"Just for comparison Uncharted 4 was 20x bigger than Splatoon 2. This shows the huge difference between Sony's first-party games and Nintendo's first-party games."