Chris,
AWS states that it is your responsibility, regardless of if you do or do not receive the notification, to keep track of your renewal date.
The good news is, and I do not know when this took effect, there is a 60-day administrative extension period . If you hustle, you will not have to retest. :-)
"Please note that it is your responsibility to renew your certification before it expires. If you fail to renew before the expiration date,
your certification is expired on your expiration date. If you exceed the 60-day administrative extension period (from your expiration
date) to renew, you will not be allowed to renew your certification and you will be required to test on all three parts of the Welding
Inspector examination to be recertified."http://files.aws.org/certification/CWI_SCWI_renewal_pkg.pdfjrw159