I have had horses in SEVERAL of the Friesian registries - I could give you a quick overview…
There were TWO main purebred registries - one was Dutch based (FHANA which is the North American secretarial arm of the FPS which is Holland). Then there was a German based registry, and the American branch was FPZV. Kind of like Warmbloods - each region/country had its own registry… VERY different registration requirements, and VERY different stallion testing requirements. I actually had one horse with each of those registries, so was kind of forced into learning about them… One allowed cross breeding, the other did not.
Over time, the German registry kind of faded out, but the American branch morphed into its own separate registry.
Meanwhile, there was NO place for Friesian crosses (although the German registry did allow it, AND there were plenty of horses that were cross bred in spite of the rules), so many decades ago, one person started up a cross breed registry, which grew like crazy, and developed a strong core of volunteers as well as a registry director (that was the Friesian Sport Horse Registry, NOT to be confused with the Friesian Sporthorse Association). It was really best when we only had ONE cross breed registry - a few started up and failed over the years, or maintained with just a handful of horses. Then…
Things fell part with that FSHR registry about 20 years ago (really related to the husband of the founder of the registry - another of those gory stories with criminal acts that has nothing to do with the actual registry, but caused a lot of collateral damage), and the volunteers all left and started up a new registry called Friesian Heritage Horse. I was part of that original volunteer base, and eventually moved over to the FHH as a volunteer too. Most of the horses followed that registry, since it came with the committed group of volunteers that they all knew and appreciated.
Meanwhile, a few members of the original FSHR started up THEIR own registries as well for cross bred Friesians, instead of joining the bigger FHH - they wanted their own rules, their own standards, perhaps a way to set themselves apart as “better” or “different”. AND the original registry is still in business, but run by a single person, and really not adding many horses to the pool, but still around with the original horses. So there you go, several cross breed registries. Way too many!
Clear as mud? It is a bit like figuring out all the Warmblood registries - there are just a lot, with different rules, different fees, different administrations.
There are also several Andalusian registries - but they don’t all start with “A” so they are spread out and it isn’t as obvious. And of course, several Warmblood registries.