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Users choose to either only 'import new' occurrences that do not already occur, only 'update existing' occurrences, or both import and update at the same time.
When using 'import new' occurrences, all occurrences that already exist are ignored.
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When import/update occurrences in different item list, indicate the column number that defines the item list and choose the Item list from the drop down. Note only one items list can be updated or imported per excel task.