How does it work with larger purchases like a kitchen or new house? Bought kitchen/house in July at 16% and still get it delivered/built next year, is it still 16% or a price adjustment?
What do you mean by "bought house"? Really bought the finished house? Then possibly 16%, provided completion in 2020. If you mean "signed contract with general contractor," house construction takes place in 2021, then 19%. If parts are completed and billed in 2020, those parts are at 16%, provided the tax office agrees (the special case is discussed in another thread).
Another example, the kitchen. Offer and signature in July 2020, delivery in May 2021. The offer will show 16%, but you will pay 19% in May 2021.
Privately, you always buy the net merchandise value plus the VAT applicable at the time of delivery/performance!