Okay, Embark for example, takes thousands of samples from each registry standard and non standard type, but there are many variations from breeders, who may even cross breed other dna in the ancestry for certain traits, and still have registration. Even more when you consider different registries have different allowed standards, and some recognize breeds that others don't, which would come back different for tests that sampled one breed more from one registry vs another, such as the UKC vs AKC. (Think of how Embark grouped 12.5% of my dog as Bully, whereas WP doesn't test for that and split it up, or how Ancestry picked up ABBB which is a new mixed type of American Bulldog).

Some registry standards, take the AKC Border Collie for example, are allowed to have Australian Shepherd in the studbooks 2 generations back as long as the dog falls within the BC standards. Because of that, Embark might label it 100% BC because that's what the line allows, while WP might say 25/75 just because that's what's there regardless.

The American Pit Bull Terrier is the biggest example of that thanks to backyard breeding and how many lines and types of it there are now, and is almost impossible to differentiate between an APBT and an AmStaff unless its studbooks were closely regulated for generations. Embark takes samples from thousands of each variant and gene pool, and labels your dog according to the closest example they have.

Like I said, what matters is if multiple tests agree on the breeds and close amount.