Depends if you want your mead sparkling or still. If you want sparkling mead, then...no, because sorbate will kill the yeast. However if you want still mead then yes....because sorbate will kill the yeast.
If it's completely done fermenting, no need for sorbate. Now, how you know it's completely done is a trick. If it's dry, then you know it's done. But if it's off-dry, or sweet, it may need to be sorbated.
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