Formule de calcul du K0

French to English Bus/Financial Accounting

I am encountering Kn and K0 (zero I think) in the context of accounting. How does this translate to ENglish? The French also uses "PNB à K0 = PNB financier - (Fonds propres financiers * taux de substitution)" or again "Formule de calcul du K n : Fonds propres normatifs * taux de substitution des fonds propres normatifs".
the French also uses Year N or N-1 to indicate a base year and subsequent or previous ones. I am using Year N and N-1 in English: is this an error?
Thanks