There is the whole early game muddling of what is the echo and what is the blessing of light. As until late Stormblood and even then more so Shadowbringers do those two start to be separated. I want to say Thordan was also able to strip their tempering or at the very least the archbishop didn't care if he had to allow one of the Heavens Ward to die. As with how Charibert joined the Heavens Ward in the tales from the dragonsong war story: What Remains of a Knight.

I also don't think everyone has the echo or at least has the innate ability to awaken to it as any newer souls that came to be after the sundering wouldn't seemingly be able to have an etched in memory of the original final days. As most of the Scions have born witness to multiple starshowers without awakening to the echo. The WoL's 1st known chance at seeing one would have been during one of the 10yr time prior to 1.0's happenings echo flash backs of the one that appeared during the battle of Silvertear sky. Or as a child/teenager when that event would have happened naturally in their life span.