There are a number of German common nouns that don't have singular forms, but that do have a singular semantics. Most of them are loan words from other languages. They are tagged as plural.
Sometimes in German, it is difficult to decide whether a certain noun is in Plural or in Singular Feminine. E.g. USA is sometimes used in sentences as if it were in Singular feminine (though it should be in plural):
In these cases, it should be marked as congruence implies it. In a number of morphosyntactic paradigms, number is ambiguous: e.g. in the diminuitive forms [die] Mädchen/pl , [das] Mädchen/sg . As explained in the general section, manual taggers have to derive the proper number from the context and give the appropriate tag.