Permanent right to reside

I have a Romanian National who was in receipt of ESA from 27/11/12 to 28/8/16.  Before that he worked from 1/6/07 but has only few payslips.  He was accepted as qualifying for ESA under habitual residence in 2012 and paid ESA until 28/8/16 when he decided to go to college on 1/9/16 but couldn’t cope and reclaimed ESA on 1/11/16 with a backdated FIT note to 1/9/16.  He has now been refused ESA based on the fact he could not be treated as habitually resident.
Our argument is that he has had longstanding mental health problems and should now be considered to have a permanent right to reside as his incapacity for work is permanent.  Tribunal adjourned to go back to DWP who have now stated that they are unable to give an opinion on whether he would get credits in respect of a limited capacity for work as this would be by an ESA DM who base their decision on HCP report.  The also mention they cannot find evidence that the habitual test was right away back in 2012 ( but those rules were not in force at that day and he was accepted)

Also we consider that he is someone who has acquired a permanent right to reside in less than 5 years ( CPAG Benefits for Migrants handbook page 19

lwelcome any comments

Is there evidence that he was authorised to work between 2007 and 2012?  Most Romanians weren’t allowed to work in the job market in those days