I wouldn't discount the possibility of their being a ding or dent on your car missed by VW QC, I wouldn't even discount the possibility of the PDI missing it. A DBP Polo I bought from new at Colebrook and Burgess (now Silverlink Benfield) had a small crease in the metal around the front nearside wheel arch edge. The paint finish was perfect around the area. I only noticed it when I was giving the car it's first wash a week after pick-up. Took it back and they agreed that it must've been there from the factory and that they'd missed it at PDI so they were liable to put it right (i'm glad they didn't try to say that as i'd missed it on pick-up then it was my responsibility).
If you take the opportunity from the dealership to give your car a complete going over at PDI then anything discovered later which isn't an obvious manufacturing fault (like my issue was) is going to be on you to sort out.
For the amount of time a PDI takes, I was once suspicious that a car I wasn't allowed to collect for a week after it's arrival at the dealership had been damaged in transit and was being repaired. No-one admitted to anything, was just told that the salesperson was on holiday and it wouldn't be handed over until they were back.