Save the Date Address Question

I am addressing them as we speak!! I did not know whether or not to put the significant others name one the STD - a couple of people told me no - b/c it is not the invitation - I am just informing the 'official' invitee of the date to hold. Do you agree? Also - there are some invitees who I know their sig. other - but not the last name and I wouldn't want it to say 'JOhn Smith and Jane' with no last name!
Opinions on just addressing it to 'official' invitee? Thanks!!

I agree with that as well..that's what I did too..I only addressed the 'official' invitee..

except if they were married then both names I put on it