Calendar of the Seven Kingdoms

How do dates work in the Seven Kingdoms? Bitterblue mentions that Death's rewritten books have dates of publication on them, and she complains that Ashen's embroideries aren't dated. So I know dates exist in the Graceling universe. But what are they? What year does Graceling take place? Would it be called "The twentieth year of the reign of King Randa," or just "Year 478?" (I'm making these numbers up, by the way.) Does anyone know the number of the year Leck came to power?