I have come up with a new rating system to help sort out which unreleased ponies from places like Taobao are official prototypes, which are likely to be prototypes/test runs and which ponies may have been created outside of the factory from spare parts.
The scale runs from 1 to 9, with 1 being the most likely to be a prototype, and 9 being the easiest to fake and unlikely to be a prototype. Zero will be reserved for legitimate and documented prototypes, and 10 will be used to denote a regular release.
Level zero prototypes are official Hasbro prototypes, and have appeared in stock photos or other promotional media. These prototypes are sought after because they are proven to be true prototypes/variants but never had an official release.
Level 1 ponies have a unique body, unique head, and unique paint elements. These are highly desirable as they appear to be legitimate finished products, that were just not released. These prototypes would be difficult to fake, as the creator would need an official Hasbro body mold, official head mold, etc.
Level 2 ponies have a unique body, and a unique head. These are likely to be some sort of prototype or test run created in the factory.
These ponies have a unique body or a unique head. Some of these ponies may have been put together from spare parts and could be test runs or prototypes. The ponies in this level either have a prototype or accidentally molded head or body.
These ponies have unique eyes or cutie marks.
Level 5 ponies have unique combinations of eyes or cutie marks on bodies or heads. They may be misprints or test runs. Some of these ponies may have been “Frankensteined” together out of unusable parts. Any misprints would be hard to fake outside the factory.
These ponies have unique hair on an already existing head type. So far, all of these ponies appear to be haired with the regular my little pony hair, and to the regular quality and styling of the factory, but it may be possible to fake one of these prototype/test run heads, with careful rehairing and styling. These all look to be to be legitimately factory haired, based on the work it would take to remove all of the previous hair, and replace with new hair, and the fact that these type of ponies are often sold at low or comparable costs compared to regular releases.
Level 7 ponies have a unique tail, that has not been seen on other ponies. These ponies may be some sort of test runs or prototypes, but creating a new type of tail may be an easy thing to fake.
These ponies are purely a jumble of pony parts from official releases. They are likely from spare or rejected parts and are sold at very low prices. To make one of these ponies, one would only need donor ponies and to be able to make new head/body/tail combinations.
Level 9 ponies are unfinished. These ponies could be rejects, errors, or taken from the assembly line before they were completed. It would be easy to create an “unfinished” pony as all you need is acetone to remove paint.
So next time you are browsing Taobao or ebay, you can check in this list for a pony. The lower level ones above are the most unique, interesting, and likely worth the most, while the higher level ones listed are worth less, and more like fun/strange finds.