They were done as collection / commemoratives series that you purchased for certain places like famous cities series or particular famous buildings series, there were series that you could collect of special towns (they were in plastic coin holders that were held in an information card), there was a series of famous people one of those was the Brothers Grimm (my favourite one!). You could either subscribe to the full series of coins or just collect certain ones.
I have a few but not of the same series as yours, mine are made of pure silver and have little certificates with them saying they are .999 purity my Grandmother in Wolfenbuttle Germany collected them back in the 1970's.
Will dig out a certificate of one of mine later as it has the company name of the sellers on it perhaps it will give you a better idea to trace the company who made them.
