Here in the good ol’ USA we call this upgrading.
You take a NN dam and breed it to a sire of your purebred breed of choice, then the daughter to a different sire of that same purebred breed. After several 4 or 5 usually generations, your animal is upgraded to the ‘real’ registry. Very common with cattle.
No one calls the final product the NN breed anymore. They call it the breed of choice sire name registry.
The WB studbooks are predicated on a Birthplace of the offspring plus qualifying for upper or lower books within the regional birthplace registry.
No one is saying they are not great jumpers or parents of jumpers.
Simply that birth region has less to do with quality than genetic origin does.
If the genetic origin says TB, the birth region doesn’t override that somehow.
The genes are what they are: Foundation plus TB, SF, Shagya, etc.
If you haven’t noticed adding TB to WB goes in cycles and it is likely that there may be another cycle in the distant (to you) future of say a decade or so, well, history is there to teach you if you care to look.