Why is the actual cell count in the vial at PromoCell sometimes significantly higher than the 500,000 cells stated on the website?

We guarantee > 500,000 viable cells per vial. To do this, we need to freeze more than 500,000 cells, as we do not yet know the viability after thawing at the time of freezing. For technical/organizational reasons, the initial cell number may also vary from lot to lot, so 2 lots with the same viability may not necessarily contain the same number of cells.