Feasts of the LORD1 And the LORD spoke to Moses, saying, 2 “Speak to the children of Israel, and say to them: ‘The feasts of the LORD, which you shall proclaim to be holy convocations, these are My feasts..
Please note that the Hebrew name for feast is "moed" which means "appointed time".The Hebrew word for "convocation" is "miqra" which translated, means "dress rehearsals".
For the multitude of reasons explained therein, many who heed the Lord's command to watch for His return, were exceedingly dismayed when the Fall Feast days came and went this year.
Rosh Hashanah is a Fall Feast Day and therefore the dating does appear to be off as it was not celebrated in the fall, but the summer.
This new astounding insight, wherein the dating of the Jewish calendar and feast days may actually be off by a month, certainly shows that though we can know the season; no man can know the day or the hour!