Way back, the man’s name always appeared first.

It’s always Mr & Mrs (never Mrs & Mr)

I do not believe that there is a precedence for this but I could be wrong.

I did multiple Engine Searches on this (phrased the question in multiple way) and I just could not come up with anything.

If the matter is of the utmost importance, I would go to the library and ask the librarian (if you have time in your schedule to do this). The librarian would be able to direct you to a book on Social Graces and/or a book on ‘Letter Writing’ (Business and/or Social). And between both of those subject matters, you will find the correct answer ref to the Rule of Etiquette on this matter, if in fact, there is one.

Years ago I graduated from John Robert Powers – the Charm and Social Graces Program and then the Modeling Program. This was not addressed. And I have a book on Social Graces that I can not put my hands on right now; however, I do not recall ever reading any subject matter on that.

I hope that this helps.