So to be a GPL project you need to be able to trust the project to release all future releases under GPL in addition to having released existing code under GPL?
I do not like this approach:
First of, you need a crystal ball to decide whether a project is GPL or not: Some projects managed to pull off a license change before, just by asking devs whether they are ok and replacing code from devs that did not agree. Its rare, but it happens, so checking for CLAs, copyright assignments, ..., is not enough.
Secondly this definition excludes lots of projects that release their source code under GPL, including the GNU project. They ask for copyright assignment, both to defend the GPL license, as well as to be able to relicense when weaknesses in the current licenses are found. I give you that GNU is probably way more trustworthy wrt. not changing away from the free software spirit than some random company.