You are welcome.
I've never heard of that happening. Although, a friend of mine did have one of his promo-codes 'change itself' to $0 discount for all plans, probably due to a database error of some kind. I don't even think you can intentionally create a promo-code with $0 discount for all plan types. :s
One thing to keep in mind, you can activate and de-activate promo-codes, but you can not actually delete them.
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