I know what your saying about the luni-solar years AnnOMaly but why didn't the WTS. include those extra days in their
final calculation of 70 x 360 to reach to 1914 ?
Where are those extra days/months to equalize to the Gregorian calendar years of 365 1/4 days ?
A lunar calendar is a calendar that is based on cycles of the lunar phases. Because there are slightly more than twelve lunations (synodic months) in a solar year, the period of 12 lunar months (354.37 days) is sometimes referred to as a lunar year.
A common purely lunar calendar is the Islamic calendar or Hijri Qamari calendar. A feature of the Islamic calendar is that a year is always 12 months, so the months are not linked with the seasons and drift each solar year by 11 to 12 days. It comes back to the position it had in relation to the solar year approximately every 33 Islamic years. It is used mainly for religious purposes, but in Saudi Arabia it is the official calendar. Other lunar calendars often include extra months added occasionally to synchronize it with the solar calendar.
The oldest known lunar calendar was found in Scotland; it dates back to around 10000 BP. [ 1 ]
Most lunar calendars are in fact lunisolar calendars. That is, months reflect the lunar cycle, but then intercalary months (e.g. "second Adar" in the Hebrew calendar) are added to bring the calendar year into synchronisation with the solar year. Some examples are the Chinese and Hindu calendars.  Some other calendar systems used in antiquity were also lunisolar.
All these calendars have a variable number of months in a year. The reason for this is that a solar year is not equal in length to an exact number of lunations, so without the addition of intercalary months the seasons would drift each year. To synchronise the year, a thirteen-month year is needed every two or three years.