If nobody will be unhappy just because his name is missing in `@author` tag of a file, then it's ok by me. I personally like how it's done in https://github.com/Behat/Mink#contributors. They don't waste own time (by tracking who is author to what) or contributors time (by forcing them to add them to `@author` tag in every PR) and just rely on GitHub's contributors feature to automatically populate contributor stats.

For me adding a contributors with which do major changes to library in `composer.json` or in a LICENSE file is completely enough.