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So has the RSU amount stated in Box 14 (Other) on my W-2 already been taxed? 

My Scenario:

I sold a number of Restricted Stocks in 2019 that I had received from my company. The dates that I acquired the RSU's range from May 2008 to February 2014 (all Long-term). The taxes that I owed after having completed my taxes via TurboTax was significantly higher than last year's which I'm confident is a result of selling the above mentioned RSU's. A coworker of mine is telling me that I may have been taxed twice? It doesn't appear that I was taxed when I sold the RSU shares since I received the total value of the shares when sold (minus commission fee). Did my employer tax the shares when they vested possibly?

If possible, please speak to this.

Thanks so much in advance!