Since that time, now, in October 2016, 105 southern small whites have been observed, at various places in the south of Limburg province.
This species used to live only high up rocky mountains, in, eg, Switzerland, Morocco.
Recently, to their surprise, biologists found it had extended its biotope to rock gardens around Zürich, and was common there. There are many rock gardens in many countries, making it possible for the species to spread further.
For the, often subtle, differences between white butterfly species, see here.