Groningen - Permitted Outcrosses
Currently MBL only accepts a few listed breeds as permitted outcrosses. Any of the Dutch Warmblood's, mainly the riding type aren't currently allowed and after some digging around and countless terrible translations that didn't make an sense whatsoever, I've found a section listing studbook/breeds that are allowed to be registered as a Groningen, KWPN being listed as one of them.
There's also multiple pedigrees of approved Groningen horses I've found who has at last one parent that is a KWPN.
(I'm really not sure how I managed to miss this for 3 months oops) This is accepted! Thank you for your research (and your patience!)