Yep. That's the definition of rolling thunder. Your PB days "rolled" to your next RES days, thereby making you available for another GS...hopefully to repeat the process again and again!

If you're junior in category you can game it a little bit by bulking your X days near the end of a month. This way all the senior guys have gotten their G#1 or #2 just in time for you to come up for a big stretch of X days. Then, if you get a GS and don't have any RES days left, all those days go in the bank for future use/flexibility. If I recall correctly, this is how Denny managed to put together a small fortune a few months ago despite being junior in category.

Happy Hunting!