It does have it, but older version Code: 10586 -> 4.6.1038.0 4.6.1 RC -> 4.6.1040.0 4.6.1 RTM -> 4.6.1055.0
They might update it within the cumulative, or just consider the current version good enough i vote for second
I just installed Win 8.1 Core and upgraded with my 10586 AiO "Home" with "kb3120678" (partially) used. I forgot to copy over the "replacement manifest" files to the sources folder But i can report, upgrading went just fine. I will retest the procedure using all files from the kb EDIT: Murphy78, I now have copied over alle files from kb3120678 and did a new upgrade and all went just fine. I don't know if you still are experiencing the errors, here it upgrades without any errors from 8.1 to 10586.
Currently downloading Cumulative Update for Windows 10 Version 1511 for x64-based Systems (KB3116908) winver now reports OS Build 10586.17, previously .14; oh, and reboot required too. edit: fixed formatting issues