When I first started looking for a Golf in April/May last year there were a few around to choose from, but nothing with any decent spec. Due to this I placed an order for a new one at the start of the summer thinking I would continue to look for used in-case something came up. The delays on mine started and when I cancelled my order I threw myself into the used market significantly all the way through to December.
As the time went on it became abundantly clear that all that was hitting the used market was ex-VW cars being sent to dealers from their fleet (these cars are easily identifiable by the KX (or other K* prefixed number plates)), or ex dealer demos for silly prices. In December when I had lost all hope of finding one, I had visited several dealers and they all told me the same story, they are simply very rare and in short supply because WLTP delays meant people were hanging onto their cars and nothing was going through the networks.
I count myself very lucky that my new car arrived unexpectedly when it did, else I'd still be sat here now without a car.
Having had a look at the market again this morning (before writing this), I can see stock has dried up even further, all the cars I looked at have gone, and the same uni-old cars are still for sale (mainly low spec, red or white) on the AUC locator, and some of the high spec silly price ex-demo cars have also gone. There's very little been added to the search results.
If you're fussy about what you want, and are in the used market, there really is very little too choose from. What I'm also seeing is the discount being offered off new is also creeping down from the 15%+ from last year, it's already at circa 10%.