I completely agree with you, based on the data it is quite certain that it is a type from the 2nd half of 1954 as you indicated and that there is an incorrect registration in Belgium.
That provenance research isn't to know the car's pedigree (although it can be interesting).
I bought this car from a Dutch dealer who in turn bought it from his heir from a barn find after a death.
As a result, there were no papers and registration number with the car.
The car must therefore still be officially imported into the Netherlands from Belgium and without papers, the RDW must therefore determine the origin and determine that the car e.g. not registered as stolen in Belgium. and if the car was already allowed in Belgium, it will not have to be inspected here in the Netherlands.
Is also about payment of tax (wouldn't be necessary for this car based on age).
if provenance research does not cause any problems, the car can be labeled and I am sure that when it is completely refurbished, I can simply get a registration number for the car.
So if I don't do research and fix the car first, I run the risk that I won't get a license plate.
Incidentally, it costs 270 euros for that examination and another 120 extra to have that check-up at my door instead of having to go there by car.