That’s the mysterious part of marketing, you just don’t know what is the right sequence, right number of mailers, right message, etc., but through testing and measuring, you can find out what will work in the marketplace you are targetting.
You need to test everything; your message, your offer, your call to action, your headline, the number of times you mail something (repetition), how you send it (postcard or direct mail).
There are alot of variables that you can test, and you need to, if you want to maximize the returns on your efforts.
NOD = Notice of Default, NOS = Notice of Sale. First one is when the bank notifies the home owner of them being in default, and the second is when they are informed of the sale date of their property.