bugbug is a platform for machine learning projects on Bugzilla data (and other data about Mozilla's processes, but this bug is mostly about the Bugzilla part).
In order to train models on Bugzilla data, we need to download it, especially historical information.
This is a bug tracking all we need to make it possible to train models effectively.
Bug 1513955 is needed because for some models we can't use the current state of the bug, but we have to train on data from an old state. For example for untriaged bugs, we can't train a triage model on the current state of the bug (which is a state where the triage has already happened), but we have to train on the state of the bug at the time the bug was filed. In order to train on a previous state of the bug, we currently 1) get the current state; 2) get the history; 3) play back the history. All bugs blocking bug 1513955 are making this more difficult, making the history inconsistent.
Bug 1528994 is needed because we need to be aware of all past tracking decisions.
Bug 1508695 is needed to have consistent data about tracking flags.