@ZapAppleMedia C-029A is the common code to identify MLP products, (almost) all products have that hard-printed on them, usually included in the mold. If you look closely, most of your ponies should have C-029A printed on them somewhere. It could be that other Hasbro products (like GI Joe) have the same code, but I don't have any other Hasbro items myself.
The pony you have probably lacks a normal code because of one of the reasons described in the article:
- The figure is a factory reject before the code printing process took place (mostly on eBay figures)
- Figures in some series or some countries don't recieve codes
- The figure is a factory error
I hope that helped