The ticker "CDT" has been taken by Cassubian Detk since July 2014. CoinDash exists since March 2017. Who was first? Who didn't check if the ticker is free? LOL
It doesn't matter, Cassubian Detk isn't listed on any major exchanges and CoinDash is, so the CDT goes to CoinDash. If you don't believe me, type in $CDT on twitter and see what results you get. Also, see which project pops up when you type CDT on coinmarketcap. It's not first come first serve in crypto. There have been many of "tickers" that were used in 2013-2015 and many of those projects are dead, it doesn't mean a new project can no longer use those tickers.