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For the first Skyline Tower I didn't know I was to receive a Trade Union item as a reward for finishing it fast. So, I didn't bother to do so. Also, I wasn't aware of the importance of this item.
As my cities grew, I'm now at the point where I've built a second and a third Skyline Tower. I constructed these really fast, because I had everything that was required. However, I didn't receive any Performance Medal. Is this item unique or am I supposed to be rewarded for every Skyline Tower I build?