Had my 407 replaced with a 408 just a couple of months ago with ~11,000 miles. It had >3/32 so I got 100% and left with a new tire - no charge. The bulletin does NOT relate to specific VINs and I never received a letter. Here's a link to the actual bulletin:
http://board.mcnews.com/Attachment69.aspx
If you go in complaining of noise, vibration or a poor ride (as stated in the bulletin) it will likely qualify. They will evaluate the tire - BE SURE TO GO IN WITH THE RIGHT AIR PRESSURE, as I've heard some who are denied due to the improper pressure/maintenance. The amount of remaining tread (also as specified in the bulletin) will dictate the coverage amount.