The 27 number includes all of the Mexican and Central American "subspecies". Most of the divisions cited in the original post were made on the basis of small differences a few highly variable physical characters. Recent genetic work using DNA has basically found little or no difference between many of these putative subspecies. In addition, as Gadfly notes, whitetails have been moved all over the United States to restore extirpated populations and augment small remnant populations such as those he mentioned in the Ouchitas. Prior to the CWD outbreaks, whitetails from Texas were probably exported to just about every state in the U.S. that originally had whitetails.
Some ecotypes such as the Coues whitetail (which includes the Del Carmen whitetails), Columbian whitetails and the little key deer in Florida are somewhat genetically distinct from other populations from which they are geographically isolated.
Genetic studies to date have shown that most "subspecies" of whitetails exhibit gradual, continuous genetic variation across the so-called range boundaries. Deer in the center of one subspecies range may look a little different from deer in the center of an adjacent one, but in the absence of geographic isolation, there is no clear line of demarcation between the two.
Much the same situation has been found in mule deer to date. For instance, the desert mule deer is not really genetically distinct from Rocky Mountain mule deer. The physical differences that we observe result from different environments acting on what is essentially the same gene pool.
