Let's blame it all on the companies.
Yes, greggii is absolutely wrong in these cases. What we do in cases of hybrid plants is list only the genus and then show the parentage in the parentage field of the entry. We also list some names in the also-sold-as field when the epithet is incorrect but is commonly used.
I'm going to let Marilyn propose the edits or merges for these names, but I will make sure that all of them are covered. Your work in finding all of these is greatly appreciated.