I think I answered my own question
Publication 502 states below:
What Expenses Can You Include This Year?
You can include only the medical and dental expenses you paid this year, but generally not payments for medical or dental care you will receive in a future year. (But see Decedent under Whose Medical Expenses Can You Include, later, for an exception.) This is not the rule for determining whether an expense can be reimbursed by a flexible spending arrangement (FSA). If you pay medical expenses by check, the day you mail or deliver the check is generally the date of payment. If you use a "pay-by-phone" or "online" account to pay your medical expenses, the date reported on the statement of the financial institution showing when payment was made is the date of payment. If you use a credit card, include medical expenses you charge to your credit card in the year the charge is made, not when you actually pay the amount charged
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The document doesn't reference when the expense incurred or treatment took place. It does specify the date of the payment is the only year in which it could be deducted. However I find the last sentence on credit card payments contradictory here. It seems to indicate the opposite...the date of charge is the year of deductibility. The previous sentence indicates it is the date of the payment when it comes to paying online or making payments. We weren't in a formal loan agreement...the business just let us pay monthly over 12 months.
I'm leaning towards deducting on the state side but I do feel it's ambiguous. If I were to amend it I don't know that I would feel comfortable deducting the WHOLE bill that year either because I didn't pay it all that year.
Thoughts?
Also...a PS my state rules basically refer to the IRS for guidance on that. So it's just following IRS rules and the difference is a lower exemption amount which makes itemizing more possible