@TheQuietMan
Sadly not uncommon.
Many times IRL many people loose ancient knowledge because the very fights and/or isolation often do the job on itself.
Teotihuacan for example is a notable example. While the ruins are so beloved, there’s no hiding regarding the fact no one actually knows what where their language or social organization. No one actually even knows why was it abandoned, for all the mystical aspects the actual historical accounts are terribly lacking. The only constant is that Teotihuacan was abandoned around the start of Mesoamerican Post-Classic period, the period of decay and the societies turning into militaristic societies compared to the slightly more commercial Classic period.
Or the Greek fire, a fire that could get much more wild when touching the water used by Mediterranean civilizations and widely popular among the Bizantine empire, and no one apparently could even save a piece of info that could help as a recipe.
The dragons seemed to put so much weight in being spartan like “strong society” they probably even forgot what they could have done themselves in the past. Isolation and constant war could actually lead up to missing old knowledge.