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.