In order to distinguish between "GPLv2 only" and "GPLv2 or later", they can't just parse the LICENSE file, they need to look at comments in the actual source fi

In order to distinguish between "GPLv2 only" and "GPLv2 or later", they can't just parse the LICENSE file, they need to look at comments in the actual source files to see if they contain "or (at your option) any later version" or some such disclaimer. This could lead to a lot of false positives and false negatives, especially if the project contains third-party code. Setting the license manually, of course, would solve the problem.