mamba
Legend
History does record the name of kings, generals, etc. at least, unless you go back a thousand years plus. What’s more, setting books can be very clear about what happened when without losing anything to the two thousand years that have passed between the event and today.The vast majority of human history is unknown to - everyone really. Most events pass by unremarked and unrecorded. And even when they are recorded, most people only know local stuff (and a lot of that is wrong). Even professional historians have specialisms and don’t know that much outside of those.
Your dragonborn might have been foot soldiers, but they did not have an empire or a royal line even with ‘regular history’, and even more clearly so in a setting book.
You can always squeeze some things in, but fitting a small tribe in somewhere that pretty much never got noticed is not the same as having an empire with an expansive history. If you want the latter, you need to retroactively change the setting or create a new one