The version you are running is in fact an ES (engineering special) as you nicely
noted You should be fine to move forward with your suggested upgrade path.
From the doc you linked;
Notes about Engineering Specials (ESs), Service Updates (SUs), and Windows Service Release (SR) Upgrades
If you run a Linux or Windows Engineering Special (ES), a Service Update (SU), or a Windows Service Release (SR) for any version listed in the "Direct upgrade" tables in the following Supported Cisco Unified Communications Manager Upgrades, you can also upgrade to the target version for that section.
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The short answer is that you don't.... That isn't entirely true while at
the same time it kind of is, but for the most part you don't configure
the softkeys. You enable or disable them via TCL. Here is the long
answer. Be sure to read the whole thing or e...
Topology: IP Phone > Switches > Microsoft NPS setup to forward 802.1x
proxy to > ISE 2.1 patch 3 Authentication: EAP-TLS using Cisco MIC SANs
Phone Models 802.1X support? 802.1x flavor Addtl Comment EAP-MD5 EAP-TLS
Cisco 3905 Y Y N Cisco 6911 Y Y N Cisco ...