For a formal wedding, using place cards on the table, the names should be preceded by their prefix, like Mr., Ms., etc. For a more casual event, like the rehearsal dinner, the prefix doesn't have to be used, unless the bride requests it.
Before beginning, I would discuss this with the bride and make sure she does not want the prefix used for the place cards, and you can ask about the rehearsal dinner place cards, as well.
I realize you want to do the right thing, but at the same time, you want to please the bride, so this is the 'rule,' (re: the prefix) and just ask her, so she receives what she wants.
This might help:
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