I'm pretty sure cordovan and horse leather are different, even though both leathers are horse. The dying process behind real cordovan leather is far longer than the normal veg. tanning of other leathers (including "horse leather"). Plus, cordovan comes from the ass of the horse, where as normal horse leather can come from any part of the body. I don't know what the ass has to offer that the rest of the body doesn't, but I'm guessing there's some relevance. Also, the aging effect varies between "cordovan" and "horse leather" that suggests they are indeed different.
I think most "cordovan" leathers referenced in this thread are actually just horse leather (which doesn't mean they aren't good). Cordovan (the name deriving from the city that developed the dying process, Cordoba Spain), is only processed in a couple places in the world due to the lengthy dying process, and I don't think guidi is one of them, but Horween is (which carpe diem used occasionally).
Now that I think of it, maybe "shell cordovan" marks true cordovan whereas "cordovan" is simply a euphemism for horse.