So I'll just repost this image here from the TC. It says "Order is normally comprised of thirty", but it doesn't say "Order was originally established and started with thirty". What if they reduced it from hundred to thirty to ten as time passed by? This whole Dragonsong War and war against dragons was a very very long battle. If you look at Coerthas Western Highlands, you see bunch of lances on the ground. We can pretty much tell that Ishgardian Templar Knights AND Dragoons were actually fighting there.Â
The book exists to give us some basic enlightenment of information to help us to make a creative character. NOT exist as Code of Hammurabi to follow their rules or get our character's head chopped off for such information. It's a REFERENCE book for our enjoyment to read. Not Ten Commendments.
What if the soulstones that were unable to pass down were lost in those blizzard wind and mist, and were sunk underneath those glacier lake?Â
While I understand that the book gives us information about what the current status of Eorzea is, but none in the book implies as "it is impossible to attain such job and the cannot be at all attained because the book says so."
There are like only few who are going to be strict about what's in the book and call you out. But there are plenty of others who will accept and appreciate on your character backgrounds as long as it is creative and you are fun to RP with. I think we all know which type we want to mingle with in this case.
Don't retcon yet. It's not fully confirmed that it is impossible to become a Dragoon unless you are one of those ten or Warrior of Light.