M14P
I think you've raised an interesting issue here. GID44 doesn't seem to cover "refresher training" conducted by an instructor that isn't an explicit part of the training for the grant (as opposed to revalidation) of a licence or rating.
I've always logged such flights as P U/T (unless for some reason I was acting as commander). I think that's FCL's intention. What counts for future licences and ratings, and what FCL are probably interested in controlling carefully, is P1 time. I'm not sure that P U/T counts for much, unless it's explicitly part of training for a new licence or rating, in which case it will be explicitly identified as such in the logbook.