With the exception of pre-alpha materials, every time I've assumed that there was a hole or a contradiction on a large issue, I've been wrong to a certain degree. On occasion we'll have a slight discrepancy which is immediately fixed, but more often than not what is happening is that we were never given a small, but crucial, piece of information - the center puzzle piece that all those around it lock into - the canonical hub, so to speak.
I believe that the rules surrounding the echo are well known and consistently followed, but that we're left with character's interpretations of its limits and thus we ourselves are subject to the same errors they might make in assumption.
For instance, we assumed that Damelliot was a contradiction because we seem to alter his past; in reality, I think it makes far more sense that he himself is using the echo (remember, he passes out at random a lot... as did your character before someone finally diagnosed his blackouts as echo!). Reinterpreted through this lens, the story plays out a lot differently (though I'll work on that once I finish Limsa).
Another example is in the THM storyline, where you use the echo on a rogue THM student. In this echo, you see that in the past they saw a shadow and wondered who it was when in the present they finally realize that it was you... who are entering the echo for the first time. Notice the paradox?
This could be interpreted many ways:
Did we actually enter the past and thus create the time loop we often see in fiction?
Did we link minds and re-create the scene, but play it out different in real time without affecting the true history?
Did we see the true history but the characters misinterpret the meaning and how it happened as a result of the echoer / echoee relationship?
SE knows, I'm sure.
But to make it more tangible for you - our questions become
(A) When we echo, are we physically entering the past, are we seeing an instant replay of the past, or are we entering a real-time re-creation of the scene to explore in new ways?
(B) What are the exact limits of this power?
and, just because I'm still stuck waist deep in Lominsan convoluted-ness
(C) What in the seven hells is Y'shtola doing that she's able to jump around and make copies of herself and escape dangerous situations completely unharmed and none the worse for wear?