Yeast Viability

I need to make a yeast starter today to pitch into a 90L brew on Tuesday. I'm using WLP005 which, according to the packet, was made on 11th May 2016. Four packets have been in the fridge since then.

According to Brewer's Friend, the yeast is only at 36% viability, meaning I'd need a 25L starter (which seems a bit much!) Will the viability have gone that low? I used three packs last time in a starter for 80L and the yeast took off!!!

Any ideas?

Yeast doesn't seem to have the mortality that is predicted. Otherwise I wouldn't be having a problem with wild yeast here when the temperature goes below freezing for months every winter. Perhaps some of the calculations are off by a bit. Here's a little experiment by someone else. http://www.woodlandbrew.com/2012/12/refrigeration-effects-on-yeast-viability.html

May is not old IMO. I would make my starter asap. I would personally get my yeast energized and pitch part and harvest some from my starter. You won't have any issues if you get it going. Not knowing what your volume or gravity, makes it hard to know how much.