Always go to the source.
Attached is Emerson's post, which says that "ice-in...simply means the entire lake is covered in ice."
In a response on that same thread, Emerson said, in response to reports of open water, that "wind must have broken [that section] up."
So, the definitions remain the same—ice-in is the whole lake iced over and ice-out is the Mount being able to reach all her ports—but weather conditions must have led to a bit of open water after Emerson saw all ice.
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