Sam
It's not a legal requirement that an ESA50 is issued but any assessment referred to Maximus, the Assessment Provider, where one is not sent to the claimant would be seriously impaired.
There have been no changes to the ESA Descriptors and Regulations since 2013 but there have been updates to the DWP guidance, primarily in the area of Substantial Risk, so I would have a good read of this section in the mental health guide and perhaps a cursory look at the entries for each activity, just to check if there is anything significant.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems