In practice, tracking all authors in all copyright notices is quite cumbersome. Instead, often only the original author is credited here even when copyright is shared with additional contributors. A more reasonable approach is to credit all authors collectively, e.g. as “the FooProject contributors” or “Original Author and others”. However, I am not sure whether that results in a valid copyright notice as the copyright holders must be clearly recognizable.

The other reason to update these notices is if there are new authors. Typically, this is done by adding a new copyright line for each set of authors, with the most recent on top. For example: Copyright 2016–2018 George Copyright 1999, 2007–2016 Fred Adding a new line is sensible since many open-source licenses require that existing copyright notices are kept intact – so you must not update them in any way. And in the above example, adding George to Fred's copyright notice would be misleading since George did not publish any of their work in 1999 and Fred didn't publish in 2018.