The administration and maintenance of Microsoft Exchange Server to ensure secure, reliable, and efficient email and collaboration services across an organization.
EricYin-MSFT, thanks for your revert.
I tried your suggestion. It did not help directly but gave me a cue to how i could overcome the issue i was facing.
Ultimately it boiled down to manually replacing some file the setup prompted & /or pointing to the path of CU13 extract during the update to Ex2013 CU23.