Currently, my (group's) subscription looks like:

GXT Premium Support
Expires on December 20, 2012
of 175 x-credits remaining

When we don't renew our subscription, I guess the credits expire.
But, when we do renew our subscription (for all 5 members of our group), what happens with our credits?
Do our current credits expire and do we get 175 new credits? (result: 175 credits)
Or are our current credits incremented with 175 new credits? (result: 330 credits)