Question: We are trying to finalize addresses right now, and we are wondering what Save the Date etiquette is when it comes to plus ones/guests. There are a few people we are not sure if we should give plus ones to or not. Will the save the date say “Mr. X and Guest” or will it just say “Mr. X” and then the invitation would say "Mr. X and Guest?" Can it be a combination of both?
Answer: Great question! You can put "Mr. X and Guest" on the save the date if you know for sure and just "Mr. X" on the ones where you're not sure (but can put them on the invitations when it's time for that). The only bad thing is to take back - so inviting a "Mr. X and Guest" on the save the date but then on the wedding invite not giving them a guest. Otherwise, you go with what you know for the save the date and can always give them a guest later.
Also, on that note - depending on how formal you get, you can use Mr./Ms./Mrs. or you can go more informal and say Bob and Sally Smith. It's all preference and who you're inviting, too. However you do it, though, I would keep it consistent.