In the 1950s and probably earlier, there were half-moon platys. I remember those in the stores in the '60s. The 19th edition (revised) of William Innes' Exotic Aquarium Fishes notes that there were wild platies (or platyfish back then) with a dark moon shaped dark mark at the base of the tail. Innes had been issuing editions of that book (kind of a Bible of the hobby since 1938 and had been printing aquarium books for a couple of decades before.

Both Innes and Lothar Wischnath (in his Encyclopedia of Livebearers and in Swordtails and Platys are quick to credit Dr. Myron Gordon with doing a lot for the hobby in collecting many of the platys in Mexico and Central America from the 1920s and 30s on. He used a model T Ford in some cases. He is also c and in experimenting with various crosses in his cancer research. (Many adult crosses would develop cancers and some crosses are maintained at the Xiphophorus stock center so that they may be sold to cancer researchers.

A number of egg layers have been subjected to crossing experiments. Sometimes eggs were not even fertilized. Other times the embryo died - often of some sort of cancer.

http://xiphophorus.org/

A little more on Dr. Gordon:
http://www.xiphophorus.org/xgsc.htm

http://www.xiphophorus.org/100300s6/css/100300s6_1.htm

Wischnath describes a moon platy as a platys with a black spot in the caudal peduncle. (The caudal peduncle is the connection between the tail rays and the body.) Wischnath suggests that a complete moon is where the platy has a spot in the caudal and two spots to the top and bottom of that spot towards the tail. I think that is where we get the mickey mouse platys. Gordon has written of a moon and referred to the two smaller spots to the rear as satellites.

You association of variatus is relevant. Both Xiphophorus maculatus (the platy) and X. variatus are associated with shallows and spring outflows. The maculatus is found in a wide range on the bottom half of east coast (Atlantic drainage) of Mexico through Guatemala to Belize. Other Xiphophorus are found in Hondoras. Interestingly, there are a bunch of platy and swordtail types found in streams and rivers in the Maculatus range. The common swordtail X. helleri is sometimes found in the same waters as platys, but the more streamlined adult swords are more often out in the current,

X. variatus ranges further north in the Atlantic flowage. They are again certainly not the only Xiphophorus or platys types in that area. I was surprised to find that they get fairly close to the US and may be tolerant of slightly cooler temperatures.

http://xiphophorus.org/distribution.htm

Gordon notes that crosses between Xiphophorus were not always easy to get. One of the early Baensch atlases carries an image of a wild variatus. It is quite colorful. They also show pictures of X. helleri with red on their sides. One wild helleri is almost all red.

Hobby platys are often a lot different from the wild macularius. A European hobbyist (according to Innes) developed a gold platy sport as early as 1916. 15 years later Gordon announced that the yellow was a result of less melanin (smaller melanophores) This sounds a lot like the golden guppies and Endler's livebearers (P. wingei maybe).

There have been a couple of variations on the gold platys, one strongly gold and one pretty light. It would be interesting to have someone check their melanophores or lack of them. Wischnath suggests that the "white-gold" strains owe their hue to a variety of genetic factors.

Mollies are show greater differences in their DNA and in the shape of their reproductive organs. Though several of them may be again assigned to Mollenesia (molly) they are not considered close relatives of the Xiphophorus. And remember, they had some trouble crossing various Xiphophorus. So mollies probably are not a part of the formula.

Tuxedo platys and swordtails, with dark sides have long been in the hobby. So too has a almost all black swordtail. Mollies in our hobby weren't a part of that process. But as many as three or four molly species may have contributed to our different commercial hobby strains of molly.

As another aside on Gordon, Al Klee, in his The Toy Fish: A History of the Aquarium Hobby in America - the First One-Hundred Years records accounts of Gordon, as a teenager, buying guppies from a New York city pet shop about 1916. A little later,hHe also bought some platys from Hermann Rabenau, the first importer of tropical fish to the US. Gordon raised at least ten generations before going off to college.