They (recently) changed the wait period terms. Previously one could not churn a card that had had a balance on it (it was relevant for me because I was issued a card I never used). Now they imply there should be at least 16 months between the opening dates:
https://www.wellsfargo.com/credit-cards/rewards/terms/
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Eligibility for introductory rate(s), fees, and bonus rewards offers
If you have opened a Wells Fargo credit card account within 16 months of this application you will not be eligible for the above introductory APR(s) and fees or any bonus rewards offers described below even if that account has been closed and has a zero balance.
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I am not eligible anyway, but some of you can try.