It doesn't matter to me if they change the license but it looks like each source file is being licensed individually. So unless you are a mamedev you aren't going to know which all files are used in the emulation of a specific system. Even if you are smart enough to chase all the includes there are still going to be core files you miss. I think it has become more murky now. They've also granted permissions in the past to Gaelco and Capcom, I'm sure others I'm forgetting.