While ‘brand’ is an imperfect basis for a taxonomy for derailleurs and ‘country’ is truly excreable, date is enough to make strong men weep - because dates of derailleurs are always in dispute. Dates are often particularly hard for Europeans to understand, as back in the 1970’s we often got new models many years after they were released in the USA.
Despite this, the date of any ‘antique’ object is a large part of its interest and chronology is a crucial part of any story. It’s hell, but I can’t avoid it.
I have tried my best with dates - and used the date that the model was introduced, rather than the date that the particular item in the photograph was manufactured.