Of course! These are important questions for ancestry testing in general, too.
Yes, the implication is accuracy. It depends on multiple features: number of markers, # of breeds, # of individual dogs in the panel, and algorithm. As Darwin’s Ark and Embark differ on all of these features, a direct comparison of what feature matters the most isn’t possible.
But! We have ways to test what features make a difference in accuracy. We perform computer simulations to make virtual mutts, where we know exactly the family tree and how much DNA they inherited from each breed. We can then vary the marker number, breed number, algorithm, etc. to see how accurate the results are compared to what they should be.
For grandparents, ancestry is usually estimated from the tested dog’s overall percentages, assuming a quarter from each grandparent (which is not completely true). If the pup is roughly 22-27% Golden, then it is a good guess that they have a Golden grandparent. Without testing the parents or grandparents directly, we cannot find their ancestry.
If one did test the grandparents and found 95%, that could still be interpreted as full-blooded Golden. A unique lineage from the UK, for instance, might be inherently 5% different from all the U.S. Golden Retrievers in the reference panel, and that lineage difference may be responsible for the 5%. Even show populations versus working dog populations may have essential differences despite being the same breed. There is no way to catalogue every Golden Retriever lineage but the more individual dogs, the better.
For Bee’s results, I would guess the biggest difference is the sheer number of purebred Golden Retrievers she is compared to in Embark (publicly available data plus all new Goldens in their database) versus the 12 purebred Goldens (publicly available data) she gets compared to here.