Most DVDs before a certain date are single-layer. Probably sometime in 2000 or something like that. Any flipper disc with a long movie that uses both sides is single-layer, for instance. I have 2 of these, one is the original version of Amadeus.

Early Star Trek TNG discs were single-layer, I understand. You can go into the display screens and switch the bitrate readout to layer readout. That might help you find out if some of your DVDs are single-layer.

I don't know how much you trust this technician, but try out the re-config in the service menu. If you don't have any old DVDs, just try a current one, which would be dual-layer. It just takes some of your time.