I have read the section of the Samaritan Arabic commentary on the Torah. The announcement is on the Day of Atonement of the 49th year. The 50th year starts on the first of the first month of the following year. The reason the announcement is nearly six months before is to allow enough time FOR HERALDS TO TRAVEL TO OTHER COUNTRIES.
I have found the reason for changing 2794 to 2800 as the period before entering Canaan, and can prove it is secondary and very late.