Self-registrations are normal to the some degree.
Carmakers registering some new models as their own fleet cars, dumping the old ones @ the Mk change or LCI etc.
Dealers registering demo cars for bran new models, new Mks, LCIs etc.
And in the times the markets cool down carmakers usually (at least in Europe, but I guess elsewhere as well) make dealers (by very instant & short-lasting special offers) to buy outgoing MY model, outgoing Mk models, outgoing pre-LCI models etc. to build an inventory for the following weeks or months when supply will be low due to MY/Mk/LCI change. And also to move outgoing cars as quickly as they can. Since when new MY/Mk/LCI cars arrive to the dealerships, older MY/Mk/pre-LCI cars are hard to move - unless huge discounts are offered.
So, the self-registrations are usually the highest in the months just before new MY/Mk/LCI modles arrive. And with broad portfolio of models the carmakers can offer such deals & push self-registrations basically every month for at least one model.
What happens with self-registered cars? The ones registered by carmakers themselves are used as company's fleet cars - used by the employees, which can then after a certain period of time buy the car out from the company.
Cars registered by dealers are used as demo or fleet cars & sold later with discount. Others are sold as new second-hand cars with almost zero mileage, some.
The problem starts when brand new models (new MY/Mk/LCI models) are pushed to dealers for self-registration.
Unfortunately there is no data by model & by party available, so we would be able to see which models exactly were registered by dealers, and which ones by carmakers.
Innovative & unorthodox marketing & sales methods are used more & more frequently to push the car sales. The competition is fierce nowadays.