Ah, my eyes apparently missed that, thanks for pointing me to it.
Honestly, my best guess would be a mistranslation or perhaps even a writing error. Zodiark's body was quite literally separated, with different parts of it in different shards. Meanwhile, Hydaelyn's body on The Source seems complete and we don't see any physical evidence of Hydaelyn on other shards. For example, when Zodiark died, his dark-aspected aether on the 13th was released. If some aspect of Hydaelyn existed on the 13th, then it would have resulted in a release of light-aspected aether, which would definitely have been noticeable and of great interest to "Golbez". But we don't hear anything about that, either in actual events or speculations by the Scions, etc when discussing restoring the 13th. Similarly, the need to send the Word of the Mother to the 1st suggests that there was no Hydaelyn there, because if Hydaelyn had in some way been on the 1st it would have been more efficient to just do something herself rather than to:
1. empower an otherwise powerless person
2. transport them between shards
Much of which you said yourself in your first post...and I agree with you! ^^
So all in all, Occam's Razor suggests to me that this is simply an example of humans making mistakes rather than an actual phenomenon in the world of FF14.
