Chabad.org — English translation + Rashi
Torah Temimah cites Yerushalmi Rosh Hashanah 1:1: “בשנה השנית לצאתם” teaches that Israel counted years from the Exodus until the Temple was built.
English: “In the second year of their going out from the land of Egypt” — this informs that they counted the years from the Exodus.
Historical counting — the Torah’s dating formula encodes the era-marker used in each period.
The Exodus remained the reference point for national chronology until the Temple era shifted the calendar of record.