Now about the double signal , there are more and more items , such as sk6822, ws2813, apa102, sk9822, all of them is dual signal , so from the picture ,we can know all of them have 6legs,

                            SK6822                                                              WS2813

                                 SK9822                                 APA102

           First ,WS2813 and SK6822 dual signal , both of the signal is data , why 2 data signal?, it is for led strip one led is broken , another data still can work , 

which can make the led strip one is broken will not affect another led working ,but the frequency speed is same as WS2812B and SK6812. 

           The datasheet of WS2813 LED AND SK6822 LED is on the following 

WS2813

http://www.szledcolor.com/download/WS2813%20LED.pdf

SK6822

http://www.szledcolor.com/download/SK6822%20LED.pdf

           Second ,APA102,SK9822 Double signal , One is data signal , another is clock signal , which Frequency speed is much faster than SK6822,WS2813, SK6812,WS2812B,  So when big project , they will not stop because of the signal transfer too big . 

           The datasheet of APA102 and SK9822  is on the following 

APA102

http://www.szledcolor.com/download/APA102%20LED.pdf

SK9822

http://www.szledcolor.com/download/SK9822%20LED.pdf