I'm a social clod.
We got wedding gift (jointly from two of my mom's friends--one that I'm close to and came to the wedding, and one that I've only met once and did not come) about 3 months after the wedding (which is now more than a year ago). I wrote out the thank yous immediately, realized we didn't have stamps, put them in the drawer, and forgot about them. (I remember it so clearly now.) While I was unpacking a box, I found them. I am beyond embarrassed.
So I'll be sending them out on Monday, there's no question about that. But I'm wondering if it would be tacky to stick a note in them (they're not sealed yet) apologizing for the delay. I'll be honest, part of the reason is for me to save a LITTLE face, but part of the reason is because I don't want them to think I didn't appreciate their gift enough to properly send a thank you.
What say you, wise etiquette gurus?

Everything the light touches is my kingdom.