Hey @KAR 
Yes, a message like, “Your card was successfully charged but was not able to store for future payments,” would be appropriate for this scenario.
An important aspect of the SCA flow is that Square is only capturing the verification details and passing those along to the card providers who actually validate that information and decide what to do based on that. Those card providers may have different criteria for whether to accept a payment or card storage request, and failed verification does not necessarily always mean that the request is explicitly rejected — in some scenarios, the card provider may decide that there is sufficient information to determine that it’s a valid request despite mismatched verification information.
Hope that clears up why this scenario can happen!