Yes, a 13th month was added every few years to line up lunar and solar calendars.
Seven_0 from post 249: You are saying that the little horn ruled from 538AD to 1798AD or 1260 years.
What allows you to use 365.24 day per year instead of the 360 days per year that you insist on?
• Solar year = 365 days or 12 months/lunations long.
• 1st Lunar year = 354 days long, or 12 lunations long. (Eleven days shorter than the solar year.)
• 2nd Lunar year = 354 days or 12 lunations long. (Now 22 days shorter than the solar year.)
• 3rd Lunar year = 384 days or 13 lunations long. This now catches up with the solar year.
Read the evidence in Ezekiel for yourself. And, IF YOU DON’T UNDERSTAND IT, read what other people have written on the subject, who do. (Del/7)
https://www.creationcalendar.com/CalendarIssue/15-The13thMonthInEzekiel.pdf
https://calendarofscripture.com/2018/10/17/do-we-ever-find-a-13th-month-in-scripture/
https://www.worldslastchance.com/the-thirteenth-month-in-ezekiel.html
https://thescripturalcalendar.com/364-day-360-day-and-365-day-calendars/
https://www.the13thenumeration.com/Blog13/2013/08/11/ezekiels-13th-month/
(part 1 of 1-3)
https://www.1260-1290-days-bible-prophecy.org/cn1a-360calendar-40year_cycles.htm
(part 2 of 1-3)
https://www.1260-1290-days-bible-prophecy.org/cn1b-360calendar-40year_cycles.htm
(part 3 of 1-3)
https://www.1260-1290-days-bible-prophecy.org/cn1c-360calendar-40year_cycles.htm
An interesting thing can also be seen with 1260,1290,1335 if one knows what day Christ was born.
One of those numbers can represent His birth day.
The other numbers can represent other Appointments He taught Israel..
And blessed is he that waits and comes to the 1335 days..