continued in support group following ESA review

My wife has just received notification from DWP that she will continue to be placed in the support group ESA following a review 15 months after transfering from IB to ESA.
The DWP were unable to give me the next review date for my wife as they said there was not one on their system,but they did on request send ESA85A(within 3 days!)which states that my wife's condition is unlikely to improve in the longer term,and the prognosis states quote 'I advise that work is unlikely in the longer term',but there is no mention of a review date.
I am rather confused with this scenario,as i understood that a review date had to be provided in the case of ESA.,and i would appreciate advice as to what to do next.
Thank you very much for the information that this sites provides,which has once again given incredible assistance not just to my wife and I,but to so many people in similar positions.

Thank you for letting us know about your wife's 'good' news.

Unlike DLA, ESA is an indefinate award that can be reviewed at any time. However, it is usual for the paperwork to give some idea of when t expect reassessment. We believe that the longest period of time is 3 years, and would expect someting approaching that for people who have been judged unlikely to improve 'in the longer term'.

There could be other forms associated with your wfe's claim, this FAQ might be helpful

ESA medical – what forms to ask for?

Failing that, you could make a 'subject access request' for all available paperwork.