It is still good. The manufacturer guarantees that SN is good for at least 3 years after you open it as long as you store it properly. Store it in an airtight container and keep it away from heat and moisture. It turns into sodium nitrate very slowly after prolonged exposure to oxgen.
" Chemtrade suggests that under proper storage conditions, the shelf life for dry sodium nitrite is at least 3 years. While sodium nitrite may cake, clump and harden within 6 months of the manufacture date, the chemical assay will remain within manufacturing specifications for at least 3 years. The table below summarizes the shelf life across Chemtrade's dry sodium nitrite product line."