There’s been a new Lync Server 2013 January 2017 CU update 5.0.8308.984 released 18/01/2017 looks to be a critical one for Emergency calls with E-9-1-1 fix !
The CU looks to address issue with Emergency Calls for E-9-1-1 so this may be of high interest to get deployed asap. It also notes It improves the reliability, stability, and performance of Lync Server 2013 web components server which cant be a bad thing 
This E9-1-1 issue seems to have occur after applying the November 2016 CU it mentions so recommend you apply this update asap.
This cumulative update actually replaces the Lync Server 2013 November 2016 cumulative update 5.0.8308.974 for Lync Server 2013 web components server.
Download
Update Version Number
5.0.8308.974
Fixes / Improvements
| KB4010079 Emergency call (E9-1-1) fails in Lync Server 2013 | To fix this issue, install the January 2017 cumulative update 5.0.8308.984 for Lync Server 2013, Web Components Server. |
Lync 2013 Server update screenshot.
Updates to core components, Conferencing Announcement Service, Conferencing Server, Lync Server 2013 and Web Components for this update.
Restart Required
After installing i has prompted to restart
Databases
There doesn’t seem to be any database updates required with this CU buts its always worth checking using test-csdatabase.
Post Jan 2017 CU Install
| DatabaseName | ExpectedVersion | InstalledVersion |
| rtcxds | 15.13.2 | 15.13.2 |
| rtcshared | 5.0.1 | 5.0.1 |
| rtcab | 62.42.3 | 62.42.3 |
| rgsconfig | 5.5.1 | 5.5.1 |
| rgsdyn | 2.2.1 | 2.2.1 |
| cpsdyn | 1.1.2 | 1.1.2 |
| mgc | 1.42.2 | 1.42.2 |
Martin Boam's Microsoft Blog 