Before revision: A third option is that by the time of the Correspondence (c. 950-960 ) the Khazars had merged the two positions into a single ruler, or that the Beks had somehow supplanted the Khagans or vice versa.
After revision: A third option is that by the time of the Correspondence (c. 950–960 ) the Khazars had merged the two positions into a single ruler, or that the Beks had somehow supplanted the Khagans or vice versa.