So I know that prequalifications are not HMDA reportable if they are never consumated, but if a loan actually closes as a result of a prequalification then what would the application date be for HMDA? Would it be the original prequalification date or the date the customer brings in the address and consents to proceed with the loan?

If it's a prequalification and not a preapproval then your application date would be when a property is identified. Until then you do not have an application for HMDA purposes.