And with the promised photos (sorry!)Please see below. There seems to be a DPC at 2 and 4 courses - see internal photo. I’m sure that in at least 2 joints they’re at the vertical joints between 2nd course of bricks ie not caused by the slab. I’m not saying what you’re saying isn’t right just maybe more than one explanation.
I was told there was a DPM under the slab as I asked if I could store things on the floor. Looking at the DPC I don’t think there’s any way that it can be lapped to the membrane under the slab as the DPC is just between the brick courses.
I’m thinking of getting someone to have a look, do surveyors do this sort of thing? I worry another builder will use the immortal phrase “It’ll cost you” which it may well do but I want it to be the right thing to do!!