Dot Stool by Arne Jacobsen  

Hi there,
I bought an Arne Jacobsen Dot stool many years ago in Germany and I would like to know when it was manufactured aproximately.
It's a black veneer stool, with three legs, so it should be produced between 1954 and 1970, but... when on this period? That's the question.
I know that it is not an early production from the 50's (the underneath metal system is newer than the stools of the first series). It has the Fritz Hansen label stamped underneath the seat (Image 1), but it has not the sticker with the serial number (month and year of production) nor the plastic cover with the date stamped on it.
So, the only options I guess I could have to know a little bit more about the date of production are the plastic tips at the end of the legs (Image 2) and the rubber shock absorbers underneath the seat (Image 3).
Does anyone know when Fritz Hansen began to use those flat tips instead of the older and taller ends? Or does anyone have any information about the rubber shock absorbers?
Thanks so much for the help!
Jose
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