If you looked into the manifest then:
In the NT manifest:
/EU/2013_21/IMG/City Navigator Europe NT 2013.20.gmap
NTU manifest
EU/2013_21/IMG/City Navigator Europe (Unicode) NT 2013.21.gmap
Yeah they are in the same folder on the server named 2013_21, but the NT file is 2013.20 and the NTU is 2013.21
So I don't think there will be a NT 2013.21