Many thanks for your response, that confirms what I suspected.
The terms were used in reports from initial assessments I had prior to my course of treatment, but were definitely not stated diagnoses. They referred to the assessor's initial impression but all later reports confirmed I was simply experiencing an onset of obsessive compulsive tendencies. The CAA however seem to have focused on the passing reference to delusional thought in the earlier (preliminary) reports and ignored the fact that latter reports do not mention this.
Unfortunately getting in touch with those earlier assessors has proven to be impossible due to the passage of time, so I guess I would just need to base my appeal on the grounds that the later, more detailed and up to date reports do not raise the issue of delusional thought.
I have asked my AME for advice on the matter but so far no luck. Am I right in saying the AME should be the first port of call for advice in these matters?