The only way to sort out any genus is to buy an illustrated monograph on that genus. While nothing is really final in taxonomy, a monograph provides one taxonomist's breakdown of the genus at a given moment in time. Such a monograph invariably points out which species are being debated as to their validity. For all practical purposes the hobbyist can assume that, to the non-taxonomist, the differences that distinguish such debated species render them nearly identical.
When researching Phalaenopsis, I use Eric Christenson's Phalaenopsis: A Monograph as my primary reference. He doesn't even mention deceptrix, but his discussion of cornu-cervi would lead you to assume that he would simply include deceptrix as a form of cornu-cervi, if he would accept it at all. That's what he does with P. lamelligera. The message here is that cornu-cervi is highly variable, and to most of us its various named forms will appear to be almost identical.
Regards,
Rick
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