Quoted from MLP Wiki: In Enterplay's trading card series, Series 1 lists the sisters' pony type as both Pegasus and unicorn but not Earth, and Series 2 lists their pony type as all three and also refers to them as "immortal alicorns"; a writer and consultant for both series has stated that the inclusion of Earth was "an intentional improvement" they made on Series 2, "based on feedback and it being one of those 'could be canon' sorts of things that just plain makes sense."
You mentioned you would change it if it was changed for the official cards, it has and I am pointing out that it has. It is not my option, it is now fact that for the cards Celestia, Luna, and Cadance are all three races.
Now, I don't mind people using it as part of their own art, but I do request that people credit me as the original designer of Nyx's cutie mark. Would you mind adding some kind of credit to the image's notes? Thanks for your understanding!