I suspect they do not know, nor have such a meticulous timeline, and maybe they realize this is a problem. I wonder if they will simply avoid stories in the general era before the curse now? this season they have the missing year and the time of young Cora. Convenient for avoiding the issue.
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“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass