Hello bikelet this Gentleman appears to have had a poor posture pre MVA and is likely to have adopted some postural changes post MVA, which he will need help with, over time. However at this stage does he need further investigations, a Neurology referral, it would concern me that with your, (also a senior physio) and this Gentlemans efforts there has not been any change in the last three months, regarding his upper trap strength.
I understand your responsibility, and part of that is deciding what is amenable to Physio.
Good Luck.