If it was completed in 1957 (which it was), 2017 would have been its 60th anniversary (not 70th).
I would in any case suggest that it's a bit mean (to say the least) not to give leeway on this. The 60th anniversary was three years ago now; how many of us could have said unequivocally that it was in 2017, and not 2016 or 2018?
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