I guess you didn't really expect to get a clear answer Legate, so I'll remain speculative.
I would not go for the late writing choice, since it would seem strange that Gandalf wouldn't mention his presence in the area or would not consult him on the problem of Dol Guldur.
I'd just ignore this late writing that isn't in accordance with any other source and go for the old southern location.
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“The invisible and the non-existent look very much alike.”
Delos B. McKown
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