Quick etiquette question - do you have to use the bride and groom's full name on the Save the Date card? I'm sure that's traditional but I didn't know if there was some leniency nowadays. For example, if the groom goes by Chris instead of Christopher, is it a big deal to just use Chris Lastname on the STDs, and use full name on the formal invitation later? Or should you always use full names on anything you send out to your guests?