I once heard every 19 years it is the same. Is this true?
If you look at the time of Molad it would be even truer, but because our current calendar can be pushed off by up to almost 2 days to avoid Yom Kippur being on Friday or Sunday or Hoshana Rabba on Shabbos, hence this can push off date of Rosh haShono by up to 2 days, so not always identical every 19 years, but always within 3 day span.
Due to this ovelapping, 8 & 11 years later, tend to be very close.
This year shall be earliest since 1899, becaue Molad Tishri is less than 1&1/4 hours away from the cut offline.
By the way, Birkas haChamo is every 28 years, not 27 years. But 27 years apart tends to be very close in date, being 19+8 years.
Some Far East religions utilize an 84 year system. Again this is (4*19)+8 years apart, and is extremely accurately close.