Does it really matter that much to you? I was just curious what other people thought, not really looking to get attacked. Her breed doesn't matter to me, you could call her a mutt for all I care. So if you could please back off from calling her owner and me a liar that would be greatly appreciated.
And they weren't lying. Art Deco, her grandsire, is registered Oldenburg, she does have Oldenburg blood, and her size and build looks like an Oldenburg so that's what they went with.
Supermane is right. Call her whatever you want but be truthful about it. She may get accepted into the NA version of the Oldenburg registry as their requirements are less strict or AWS but until you get the horse registered into whatever you choose she is a grade warmblood.
Personally I don't care other than there are too many people calling their horse whatever they choose and when they sell them and they are leading the buyers into a false premise. My own horse has TB blood in it two generations back and he also looks somewhat like a TB but no way would I claim he is TB.
Just look at Craig's list for a ton of false advertisement. Even you were sold a horse under a false definition.
If you have a nice horse why put a wrong label on it. Enjoy it for what it is...a nice horse.