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The best thing to do is to get them new dishes unless you can somehow discern which dishes were used for which foods before they were moved.
The only other alternative is to consult a rabbi to see what he says if you want to keep the same dishes
They could possibly be koshered to make them able to be used again for separate purposes.
Koshering includes heating the item with a blowtorch or immersing in boiling water. The method used depends upon the type of utensil and how it has been used. After deciding with the Rabbi which utensils will be koshered, an appointment should be made for him to come and kasher your kitchen.
This could be a cumbersome process.
Thus, getting new plates may be the easier answer.
Actually Linda, I've since spoken with a Cantor, and honestly your answers are not solid, I got better answers on Google in three minutes. I came to JustAnswer to get a solid answer.
I'll accept your answer, but it's not a comprehensive or well researched answer.