I'm very confused on how to check if a program is GPLv3 or GPLv3+.
Looking at gnu.org website it seems (to me) that there's no difference between the two: there's only one license text (http://www.gnu.org/licenses/gpl-3.0.txt) and the declaration to insert in source headers says "either version 3 of the License, or (at your option) any later version" (http://www.gnu.org/licenses/gpl-howto.en.html)
So how to distinguish between the two?