My apologies for the late reply.
A possible approach to disable items that have already been selected is to use the items method of the Grid in the save event to get the values of the DropDownLists. You can add them in an array, which you can store in the localStorage.
Then, in the open event of the AutoComplete, you can add class k-state-disabled for every k-item element, whose text is equal to an item from the selected values which I stored in the array. You can see the suggested approach in action in this Dojo example.
Let me know if that works for you. Feel free to get back to me if you have any questions.
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