Non-accession definition
Non-accession reckoning means that the year in which a king died and his son succeeded him on the throne was counted as “year one” of the son’s reign, even though it generally was not a full year. Under accession reckoning, "year one" of the son’s reign did not start until the first New Year's Day that the son was on the throne. The SO and the Talmud assumed non-accession reckoning for Judean kings, but it has been adequately demonstrated that this was not always the case throughout the monarchic period (Thiele, pp. 56–60, 77–78), so that it is necessary to con- sider carefully each time-period to see if accession or non-accession reckoning was assigned to the king's reign. The decision of which method to use may have depended on the whim of the king, and any approach that assumes a priori that one or the other method was always used is bound to end up conflicting with the biblical data. This is a point of considerable importance, because the assumption that the reign of Zedekiah was measured by accession reckoning is prob- ably the main reason that many have placed the fall of Jerusalem in 586 BCE instead of the correct 587 BCE. For a recent study that examines all texts in the four books of Scripture that give chronological data for this event and shows that they all point to 587 and not to 586, see Rodger Young, "When Did Jerusalem Fall?" Journal of the Evangelical Theological Society 47/1 (Spring 2004) pp. 21–38.