Using old and fresh yeast in a starter

[BeerPal]

I have a vial of WLP001 that is 4 months past its "Best By" date. I'm going to make a starter tonight using fresh yeast, but I wonder if there would be any harm in pitching the old vial to the starter as well.

[BigNastyBrew]

Probably not, but I could just be guessing. I would calculate viability of the old yeast and the new yeast separately and average the 2 to figure overall viability and make a starter based on the average but with inputting 2 vials into the mr malty calculator.

That's just me though.