59 is the year as the month was "usually" applied by not required. Required marks were the Eagle w/ appropriate character/letter, mark of the proof facility(Eckernförde as Oak leaf from 1952) & the year of proof, sometimes w/ the month. I believe it was 1968 that saw the use of characters for the year. Also me thinks Eckernförde was a satellite stamping station & Ford has some additional info.

Cheers,

Raimey
rse