I also would suggest that the use by dates are calculated to the particular strain, which is why you may get different ranges based upon each strain. Given my counting variability of +/- 3 billion cells and assuming that commercial packages are all the same, I would contend that they plan on at least 100 billion cells at the best buy date on the package. This would equate to 98 billion cells in the package. Projecting this out, at 6 months (26 weeks) the viability would have dropped around 10%. If you look back at my last post, I had a cell count of 109 billion cells with a viability of 98% (rounding down) which would give me 106.8 billion viable cells in the package at 5 weeks old. This really throws all the calculators out the window when it comes to predicting the number if viable cells based upon manufacturing dates. Like all manufacturers, the yeast companies have made process improvements and lengthened the shelf life, viability, and survival rates of the liquid yeasts. While this may have been the case 14+ years ago when most of the yeast calculators we use today were developed, the world does not remain static. Likely the same reason some yeast manufacturers have stretched out the acceptable ageor their ueasts, maybe improving something in their process allowing them to assure acceptable viability/vitality for a longer time. Many homebrewers believe that vitality is much more important than cell count and report good results using vitality or SNS (shaken not stirred) starters. I'd rather this than the opposite, especially since most of us don't know how the yeasts were handled and stored before they came into our hands. This way of aging would favor erring on the side of over pitching in most cases. Since the pitching rate and starter tool doesn't specify brand names, we can assume the aging is still calculated in the same manner as in earlier versions. Several yeast manufacturers have stretched out the age they consider their yeasts as still being pitchable for a standard batch.

IIRC, that would be 90 days before the best by date for liquid yeasts and 2 years for dry. It appears the BeerSmith ages yeast based on the packaging date.

Beersmith 2 vs 3