Searching For Horse Pedigrees

I used to know a horse named Mitten, I've probably blabbed about him on here. I loved him to death, but he passed away. If you guys haven't heard of the PonyApp, you can make profiles for your horses, log activities, takes notes, upload pictures. Of course I had to make a profile for Mitten and so I contacted this woman who used to know him before he retired at my barn and asked about his registered name, which turned out to be Run the Gauntlet. Then I started searching for him on the interwebs and found a bunch of pictures of him. Then I started obsessing over searching the internet for him and started looking for his pedigree. I found a pedigree for a horse named Run the Gauntlet, but then I realized that there are two of them... One was the same color as Mitten, but was born in 1999, the other was a described as a chestnut and was born in 1985. Why do horse people do this?