I'm starting to wonder if all the monozygotic seeds are really zygotic. Hadyvermont PMed me saying he doubted if all monozygotic seeds are zygotic. I argued against him, though I was also starting to think the same.
It probably depends on the variety, I am guessing.
I'm pretty sure monoembryotic seeds can be nucellar.
It's a good way to help separate them out, but may not completely separate out the zygotic from nucellar.
Obviously if you have 100 seedlings and can't grow them all out, and you are only looking to keep the zygotic ones, the polyembryonic ones should be discarded. That would at least double or triple the chance that the remaining seeds will be zygotic.
It's all about probabilities and optimizing them.
Example: maybe for one variety, just hypothetically, 70 percent of the monoembryotic seeds will be zygotic, while 10 percent of the polyembryonic seeds will contain a zygotic seedling sprout. It might look something like that.
Regardless of the variety, I think it's still always a good way to help discriminate if you have many more seeds than you want to grow.
I usually write on the labels for my seedlings whether they originated from a polyembryonic seed. That information could help me later.