The DATEX II namespace for the 2.x generation of DATEX II contains the major release number ("2") PLUS the full (i.e. major and minor) version number of the tool ("2_1"). This does not make any sense and should be removed from the next version on. Instead fo this, an appropriate XML attribute (e.h. "schemaCreationToolVersion") should be introduced to indicate the real full version of the tool without hampring with the namespace.
The DATEX II v3.0 namespaces only contain the major version of the model (i.e. "3" for v3.0).