They were ordered and built during the same period, approximately (1950-1952), however I don't think we could say 'they were bought together', (a) each of the three classes you mention had its own contract, and (b) the contracts of the rolling stock you mention was signed between the manufacturer and a different railway each time... (ΣΠΑΠ, ΣΕΚ, ΣΘ, ΣΒΔΕ).
But what do you mean by that?
Georgegala wrote:(Actually, they were 18 but......)
To be so confident, I guess you have some strong evidence in your hands...