Where does the %Viability data come from? And how can I set my desired pitch rate? I'm seeing big differences in viability across a variety of calculators. For a recently manufactured PP of WLP001 I'm seeing values ranging from 71% to 96% (BS3). Not knowing the pitch rate used in BS3 really leaves me wondering how accurate it is.
The accuracy of the model is highly dependent upon the age of the yeast package, the conditions under which it was stored, actual viable yeast at packaging, yeast strain, etc. It is never perfect, but designed to get you in the ballpark. There is a pretty wide range of cell counts which the yeast can and will perform consistently and that is highly strain dependent as well.
Then you get into the models which have mostly been developed decades ago and do not take into account the improvements which have been made in yeast health, packaging integrity, and overall vitality of the yeast over the past number of years. The rate of decrease in viable cells over the age of the yeast package tends to be extremely conservative in the estimate of % viability, so the actual percentage of viable cells will tend to be greater than the models predict.
This is one reason that some of the yeast companies have switched from printing the manufacture date to printing the best-by date on the packages. I use yeast packages as a means of calibration on my cell counting technique and personally, I have never had a Wyeast package check in at less than 100 billion active cells even at 4 to 6 months old. Most clock in at a consistent count of 108 billion to 112 billion cells total (counting both dead and live cells). This correlates fairly well with the information I was able to squeeze out of the Wyeast people at HBC back in 2019.
I cannot comment too much on White Labs other than to say the two tubes I tested back a number of years ago were just a bit over the 100 billion total cells. Their new packaging probably negates anything tested in the prior packaging in terms of viability and total cell counts.