I have appliqued my labels on in the past, but now, if the backing isn't too dark, I use a pigma pen, & write directly on the backing. :-)
I usually include the name of the quilt (if it has one), my name, city & state, the date - at least the month & year, who I made it for, their name, city & state, and the occasion. So you could just put that it was made for "Dick & Jane" on the occasion of their marriage, and the year (instead of a specific date). Or you could leave a blank space for the date of the wedding & fill it in later.