Period 4 and 5 of Differential Views can take a hard-coded version. This is documented in the UI.
Period 1, 2 and 3 can also take it. The typical use case is to use a version name like "BASELINE" that each project can set in its history to be able to have measure filters based on this baseline period.
We have to update the documentation available in the UI so user is aware of this possible use case.