The Jewish calendar is based on the cycles of the moon and there are seven religious feasts that are clearly marked and adhered to.
Beginning in the spring, the seven Jewish feasts are Passover, the Feast of Unleavened Bread, the Feast of Firstfruits, the Feast of Weeks, the Feast of Trumpets, the Day of Atonement, and the Feast of Tabernacles. The Jewish feasts are closely related to Israel’s spring and fall harvests and agricultural seasons.
The Jewish new year is clearly marked in the calendar as explained in this article:
One of the “appointed feasts of the LORD” given to Israel in the Hebrew Bible (Old Testament) is known today as Rosh Hashanah, literally “Head of the Year.” We read about Rosh Hashanah in the Torah, the Jewish Law found in the first five books of the Hebrew Bible. “And the LORD spoke to Moses, saying, ‘Speak to the people of Israel, saying, In the seventh month, on the first day of the month, you shall observe a day of solemn rest, a memorial proclaimed with blast of trumpets, a holy convocation. You shall not do any ordinary work, and you shall present a food offering to the LORD’” (Leviticus 23:23–25).
Rosh Hashanah, or the Jewish New Year, is also known as Yom Teruah or the Day of Trumpets. The word teruah means “to shout or make a noise,” so this holiday is marked by the blowing of the shofar or ram’s horn in Jewish synagogues around the world. Rosh Hashanah falls on the first day of the Hebrew month of Tishri on the Jewish calendar, which usually corresponds to September or October. It always falls on the seventh new moon of the Jewish year. After the destruction of the Jewish temple in Jerusalem in AD 70, even though this feast day falls on the seventh month of the Jewish religious calendar, it began to be called Rosh Hashanah and became the beginning of the Jewish civil calendar.
Rosh Hashanah begins a ten-day period leading up to the holiest day of the Jewish calendar, Yom Kippur, the Day of Atonement. These ten days are called the yomim nora’im or Days of Awe in modern Judaism. The sounding of the shofar on Rosh Hashanah is a wake-up blast and a sobering reminder that the time is near for the Day of Atonement. It is a call to teshuvah, which is repentance and turning back to the LORD. These ten days are ones of great introspection, heart-searching and self-examination. The sound of the shofar for the Jew was, and still continues to be, a call to examine one’s life, to make amends with all those one may have wronged in the previous year, and to ask forgiveness for any vows one may have broken. So the primary theme of Rosh Hashanah is one of repentance.
Given the strict adherence to these religious feast days, no Jewish person (including non-Jews who lived in the land) would be in any doubt as to where they were in any given year.