Hardly anyone knows it but a gentleman's stationary is different from a lady's and from businesses stationary.
These days just sending a note is impressive enough but if you really want to do it up right, get some good stuff.
A woman is a person too, not merely a wife and mother, and the outside of the envelope should be addressed to "Mr. and Mrs. Novak", "James and Mary Novak", "Mrs. Mary and Mr. James Novak" or "The Novaks".
And only that if you know she prefers "Mrs".
Her social title is her name, not "James' wife".
If you were to address an invitation just to Jane, it would be to "Mrs. Novak", or "Mrs. Jane Novak", which is her name.
The fact that her husband John is also a Novak is irrelevant if she has chosen to be one. It would not be appropriate to address her personally as "Mrs. James Novak", any more than it would be appropriate to introduce her as "this is Jameswife".
If you did address something to "Mrs. John Smith", you're clearly addressing "that woman John married", not Jane herself.
Formality does not require erasure.
And to do it differently would be to address only one person, the husband, and treat their counterpart only as an add-on. That's not an interpretation, that's what is literally involved. "The mrs of john smith" applies to whomever he marries. It's not an invitation to Jane Smith nee Jones as her actual own person. If you respect Jane, you can respect her as her husband's equal, and equally deserving of being addressed by her first name. If you address her merely as John's wife, she's right to assume that's all you see her as.
It wouldn't be appropriate to introduce a couple as "this is John Smith and his wife", and it's not appropriate to address them that way.
If you respect two people as each persons, you address something to both of them, not merely to the man plus his appendage.
That was only appropriate in a world in which only men were persons, and wives were just possessions brought along with them. Most of us don't live in that world anymore, and etiquette specific to that world is void.