Compatibility licences between GiD versions

• Is a GiD version license valid with other GiD versions?

Each main version 15, 16, ... require its own licence.

We are releasing a main version every two years.
In the middle we maintain two lines: official and developer.

official versions: only contain fixed bugs, and have nomenclature *.0.1, *.0.2
developer versions: contain fixed bugs and new features *.1.1d *.1.2d

The same licence/password is valid for all official and developer versions of the same main version (e.g. all 16.x)

There are special prices to upgrade from the previous main version.