After testing an example and uploading a sketch I wanted to use one of the other examples form the list, but now the list contains only the "buildin examples". All examples related to installed libraries are no longer available.
Duplicates between the forum and GitHub are perfectly fine. The forum is a place for free ranging feedback and discussion, so we don't worry much about duplicates here (with the exception of the prohibition against a single user cross-posting the same topic multiple times)
Conversely, GitHub is a place for tracking structured bug reports/feature requests for the developers to investigate/evaluate and resolve/implement. So we are careful to identify and close duplicates within the Arduino IDE issue tracker.
I try to cross-link between the forum and GitHub in order to make all the relevant information easily accessible. Because it is too much work, we don't often keep the forum threads with news of ongoing developments, but the GitHub issue tracker is well maintained, so that is a good source of news from the developers.