Although Microsoft Level 2 downplayed issues with the Recovery Partition or EFI System Partition as a root cause, I am seeing persistent KB2961908 install failures with error 0x800f0922. It appears that this fixes is related to noncompliant UEFI modules and update dbupdate.bin and dbxupdate.bin in C:\Windows\System32\SecureBootUpdates.
If I can get caught up, I will try the ProcMon PD/PR procedure described in http://chentiangemalc.wordpress.com/2014/04/03/case-of-the-kb2919355-installation-failure-windows-8-1-update-1/ to see if anything interesting pops up. It is the only other persistent error that I am seeing other than Windows Update Troubleshooter reporting RC_DataStore ErrorCode: 0x80070057, a symptom that Level 2 indicated was not germane to this problem.