A lunar year was made up of 12 lunar months and that figures out to approximately 354 days.
A solar year or tropical year as it is called on which the return of the seasons depends is the interval between two consecutive returns of the sun to the vernal equinox, and this tropical year consists of approximately 365 days, 5 hours, 48 minutes and 46 seconds. To bring the lunar year into approximate synchronization with the seasons in the solar year, it was necessary to add one month 7 times during a 19-year cycle. This causes the variation in dates. Although it is impossible to exactly synchronize the two calendars, it is not necessary that we do.
The New Year began with the actual sighting of the New Moon of Abib, which was the first new moon after the spring equinox. Whether the preceding day had been the first or third or fifth of the week, the sighting of the new year moon meant the beginning of the year and the beginning of the week, as the first day of the new year was always the first day of the week. In view of such evidence, is it not strange that the Seventh Day Adventists can claim a succession of “Sabbath” Saturdays?