I remember drafting a recipe for you in the past:
The style is quite broad and does not really have many guidelines other than that the Original Gravity needs to be at least Plato 15.5 (SG 1.063). In the early 20th century you saw a heavy decline in the Dutch ale culture and ales were rapidly being replaced by lagers (pilsner). Many of the older breweries shut down, were bought and consolidated, or simply converted to making lagers. After WW2 you saw an even quicker decline in the number of breweries and almost all of them made pilsner (some of them Dort). Bockbier was brewed once a year as a specialty by these breweries - so they would have been lagers.
We always had a big influence of Belgian beer in the Netherlands. They carved out a niche for themselves with cafés that only served "special beers" (not lagers) in the 1970s. This quickly caught on and led to breweries adopting many of the Belgian sensibilities into their beers. This lead to many variants that were top fermented with Belgian ale yeasts. Belgians don't really drink bockbier, but some clever manufacturers just rebadged their dubbel to bock (or at least made very little attempt to alter it) and export it to the Dutch market. At this moment you see most mass market manufacturers (Heineken, Grolsch, Amstel, Dommelsch, Hertog Jan etc.) use lager yeast while the smaller/more craft breweries use top fermenting yeast (Jopen, La Trappe, 't ij, de Molen etc.).