How should open source projects handle copyright notices?
Copyright notices in source code are inconsistently applied and poorly maintained. As a result, such notices are poor sources of information. Should more resources be applied to the maintenance of copyright notices? No.
Copyright notices are one-line strings that typically include the word "Copyright" (or some substitute, like ©), a name (usually a person or company), and a year.
In this article, I am not focusing on licenses or license notices (which may sometimes include a copyright notice). My suggestion for low prioritization of investment in copyright notice maintenance does NOT apply to license information. License information should be clearly presented and maintained to be accurate. If you invite others to take and do something with your software, please make the permissions that are being given clear by presenting and maintaining clear license information.
Returning to copyright notices: What is their legal significance? If you think copyright notices satisfy a legal requirement or at least provide a significant legal benefit, think again. The legal significance of such notices in open source software is so small that one can easily find practical considerations outweighing the legal significance.
