EDIT

As nomenclatural sources now have there own subclass PrimaryTaxonomicSource is enough for nomenclatural sources.

Having the additional source type in the enumeration requires that this source type is always removed from source type lists (dropdowns) where it should not be an option.

Is ist in use for type designation sources? But also here it is enough to use PrimaryTaxonomicSource.

For other SingleSources the source type is not so clear but definetely it should not be NomenclaturalSource.

The only option that we could need NomenclaturalSource is that we store these sources together with the set of sources attached to e.g. IdentifiableEntity/TaxonName. But this is currently not the case.