It's hard to know for sure either way, but I have also heard the story about the symbols being added on to more common Argie ponies later on. The vast majority have the same body/hair colour base as one of the original six ponies, so it is plausible. The walking ones are believed to be unfinished ponies, but the symbols may have been added later. It has been discussed a few times on here before, but not for a while.
'Repaired the hair' was a common thing for some Argie sellers back in the day, so sadly it is entirely possible that they are later modifications. In addition, there used to be a LOT of MOC Argies around, and none of these have ever shown up on card :/
If it is the seller in New Zealand I'm thinking of, she bought them in good faith and hasn't really been around the community since we started hearing the stories.