I think after a year you're at 10% viability on that pack. I'd pitch the new pack.
If it's a year old, it's doubtful there's enough viable yeast there...especially without making a starter. That is, unless it's a one gallon batch of 1.030 beer. Even if it ferments, the stress on the yeast might cause unwanted flavors. I'd pitch the new pack to be safe.