There has been some discussion as to why the reigns of the kings in northern Israel and the kings in Judea do not line up. The reason is quite simple. They used different calendars to date their reigns.
Solomon changed the calendar from the sun-based model that Peleg devised immediately after Noah’s ark landed to the one that the queen of Babylon devised that made her the “Queen of heaven” and was based on the moon.
The Babylonian moon calendar wasn’t really a big deal in those days, as both the sun and moon had months of 30 days. They remained synchronized until their movements were disrupted, the sun slowed down to add a quarter-day, but the moon changed to its current 11-day loss of days compared to the sun. That threw the entire known world of the time out of kilter. The crops were planted at the wrong time, the fields were plowed too late, so that the rains came and stopped the process and the seeds were not planted. The weather turned into one of its cold dry cycles and the nation of Babylon collapsed. That was in the days that Jacob went down into Egypt to Joseph. The rains never came back to Egypt, so that they “watered the fields with their feet” by building irrigation canals.
When the weather turned wet again, the second Babylon came to power, and the moon-based calendar was reinforced, along with its religion that set the “lesser gods” before the Creator God, the nation of Israel was established, then conquered, and the cycles continued to repeat as nations rose during wet warm periods and collapsed during cold dry periods of famine and Rome fell to invaders, but the national system of military control survived until this day, just under different rulers.
Julius Caesar became famous for changing the calendar from the moon-based model back to the sun-based model, but he chose an Egyptian mathematician to design it, and his calculations were just slightly off. By the time of Pope Gregory XIII, the days were off from the Spring Equinox, the New Year’s day for all nations in every calendar up until that time, by 11 days. By that time, the pope was the one who legitimized all rulers, and when he changed the calendar to delete those 11 days, all nations followed the new calendar, except a few up high in the mountains, far away from the major trade routes and what we would call civilization today. The reason he chose January 1st as the start of the year was because that was the day the Roman Senate began its annual meeting, and he needed them to approve the change, which they did when he made this change from Spring to Winter.
The end result of Northern Israel returning to the sun-based calendar from the moon-based calendar that Solomon bound on the nation through the influence of Hiram, king of Tyre and ruler of all trade throughout the known world, was that Israel counted their rulers’ reign as starting on the Spring Equinox, whereas the nation of Judea started theirs on the Autumnal equinox according to the moon-based calendar that they retained from the days of Solomon. Several Judean kings tried to revert to the sun-based calendar without success, and it is still followed by the Jews throughout the world today. According to the Rambam, the sun-based calendar will not be reinstated until the remnant – not the entire nation, but the remnant – of the people of the northern 10 tribes returns to the Middle East and becomes the controller of all national trade through a gold-based monetary system that the entire world adopts as necessary to participate in that trade activity.