In my experience they dont look that deep. It wouldnt be obvious from a quick glance under the car and a look via the carpet flap that its been rung. obviously youve looked deeper.

also the DVLA man might have been in on it. Some of them are easy to bribe. For example i know of one who will give you a new VIN for a brand new cossie converted shell to be used as a reshell and updating the DVLA records correctly and use an age exemption so you dont have to get the "radically altered vehicle" through an SVA. (was a few years back mind). Once the data is on the system there is no record of SVA cert or details of inspection just that it was done on that date.