In the last couple of weeks I have been involved in a large number of cases where customers were either still on SP1 patch level or other patch levels older than April 2017 CU.
Be aware that all these servers/farms will be unsupported after April 10th, 2018!
On April 10th, 2018 mainstream support for SharePoint 2013 will end.
After this date no further (non-security) hotfixes can be requested for SharePoint 2013 and on top of this only SharePoint 2013 server farms on April 2017 CU patch level or later will be supported.
All the details can be found in my blog post about the Updated Product Servicing Policy for SharePoint 2013
So if you have a SharePoint 2013 farm on an older patch level than April 2017 CU you should plan to upgrade to a more recent patch level asap to ensure that you have a supported server farm after April 10th, 2018.