It's really no big deal to wish someone a “Merry Christmas” and then see that person the next day and repeat the process.
It's almost inevitable. You can't always know someone's work schedule or whether you will see that individual at some subsequent social occasion.
And, of course, you can't ever tell when you will simply bump into someone again and again after wishing him or her a happy holiday.
But now we're in the home stretch. You can say “Have a Merry Christmas” today without the silent P.S., “Of course, I'll probably see you 16 more times before the holiday actually arrives.”