If you make a new form, limit salutations to Dr., Mr., Ms.

Why do you ask people what their titles are at all? Dr., Mr., Ms. Why do you need them?

If your customer wants Mrs. & Miss, push back. Up to you to decide how far and how hard, but make an effort.

Given that you do ask such silly questions, who are you to push back against the title someone wants? If a woman, say my mother, older than the both of us, wants to be known as Mrs., who are you to push back on that? Is your push back a step for gender equality, or you just being even more self-absorbed and clueless in your questions than before?

Would you push back against a person that wants to identify with a different pronoun? Or a different gender? Then why are you pushing back against that person's choice of a title?

Do you verify the titles? If not, what's the skin off your nose?