So this 1 year for TY note business...

TTiger03

It's probably not likely, but I wonder if any of these brides lost cards attached to the gifts or something similar.  I'm thinking of all the threads here where brides are wondering how to find out who a gift came from.  Sometimes the response is to wait for someone to call and see if their gift arrived. 
I doubt this is the case with most of them (especially since many are discovered to not be sending any cards), but it might be for some.
It doesn't hurt to call and check that the gift arrived.

My dad's cousin called my sister to find out if her gift arrived because my sister was misinformed and didn't want to open any of the gifts until the wedding.  When my second cousin called, my sister opened the box and send the TY.  My sister was not offended by the call.

mysticl

To go with what TTiger said, earlier I mentioned the wedding I went to 3 years ago that I never got a ty note from.  I happened to be there when the bride opened her gifts.  It wasn't a big event some people just went to her parent's house for a little while after the reception and they went ahead and opened gifts.  They thanked me verbally when they opened it.  However, they received several gifts that did not have cards.  They were all from their BBB registry and guests had taken advantage of the free gift packaging you can get when you buy a registry gift there.  I'm not sure if the guests assumed the store would include a card with the wrapping or because they didn't have to shop for wrapping paper/gift bags they forgot to card shop.   So I do have to wonder if they just decided not to send any thank yous at all.