The triplets are identified by their manes- each has a different little curl from one ear, and different numbers of frayed tips. It was hard ensuring the triplets looked proper, otherwise I feared they'd look like three differently aged fillies. Pinkie Pie has fun but not THAT much fun.
We may never know where the eyepatch came from.
Pinkiemac isn't even my favorite ship. I just wanted to make something that I personally would enjoy looking at.