Admit the lateness, apologize, no excuses and comment that the lateness of the reply in no way reflects upon how much they appreciate the gift, how they've been enjoying it and glad they could be at the wedding.

I would make it clear that a first thank you note was written:

"You may have already received a thank you note from us for the lovely vase you gave us. But we found out that many of our thank you notes didn't reach their intended recipients, so I am sending this just in case. The vase goes so well with my dishes . . .

"This is an embarrassingly belated, but nonetheless sincere thank you for the lovely...wonderful..."

I was dismayed to learn that some of my thank you notes for our wedding gifts may have gone astray.

The lovely vase you sent is so much appreciated.Thank you for this thoughtful gift. I will think of you whenever we use it, which will be often, I am sure. I have it filled with hydrangea at the moment and it makes me happy every time I look at it.

Many thanks, and I do apologize for the tardiness of this note.

graywings' is perfect, imo. It notes that thank-yous were already done. Takes the burden of 'blame' off anyone & instead of leaning toward an apology for not getting a thank you it leans toward saying some might receive a double thanks (not much offense in that scenario at all). Comes off classy all the way around.

I think what Graywings wrote is absolutely perfect! There isn't a hint of blame to be found, yet it makes perfect sense.

I like graywings' example. I would want to explain that I did write notes and that many were not received (no need to go into details) rather than have people think the worst. It also helps explain why some people may receive two thank you notes.

Thank you for the advice and wording. I emailed your replies to DD and she feels much better now. She wanted to convey that she had written them in a timely fashion but was concerned that her MIL might somehow feel blamed.

She combined the phrasing from your posts and will personally deliver them to the PO....now she's crossing her fingers that the PO doesn't let her down. She may even follow up with a phone call in 2 weeks.

I knew her spirits had lifted when she said to be sure and extend her thank you to all who helped.

Thank you - officially.

Oh, I read through your original post much too quickly (ADD is so frustrating). Yes, Graywings' version is perfect!

Your DD sounds lovely and I imagine the gift-givers will be touched by her notes.