Hello Rainer:
This is a problem that researchers have encountered with Greek vessels right up to the 1950s at least.
The differences relate to the feminine form of names, and certainly pre-1939 the forms Bulgari (feminine of Bulgaris), Cambani (Cambanis), Chandri (Chandris), Coumantarou (Coumantaros), Embiricou (Embiricos), Goulandri (Goulandris), Hadjipatera (Hadjipateras), Kulukundi (Kulukundis), Livanou (Livanos), Nomikou (Nomicos), Stathatou (Stathatos), and Vergotti (Vergottis), among others, were used.
As an example of the changes that took place, in my book "The World's Merchant Fleets 1939", under the heading of Nomikos in the Greek section there is the Aspasia Nomikou, a tramp steamer built in 1938 and which survived the Second World War. In 1938 she certainly had the name spelled in that way; it was on the vessel's registration documents as such and appeared likewise in Lloyd's Register and Lloyd's publications such as "Lloyd's Shipping Index". By 1949, when the accompanying photograph in my book was taken, her name had become Aspasia Nomikos.
I have a prewar photograph of the then Evi Livanou, but a new postwar vessel named after the same member of the Livanos family had the name Evi Livanos.
Having said that, however, not all owners/vessels adhered to this rule, sometimes not even within their own fleet.
I have no evidence to support the following theory, but I would suggest that the shipping fraternity in general may have encountered the same problems and that the naming styles for such vessels in international trade were made consistent in an attempt to avoid confusion.
Regards
Roger Jordan