A dogs memory

Had a dog from 9 months to around 3 yrs old. I sold him and the guy kept him for 8-9 months. Guy calls me one day and says the dog just wont hunt for him anymore and was going to cull him.. I went and picked the dog up and as soon as I got home he headed for the pen right out of the dog box. Took him a couple days later and went to work finding hogs like he had never been sold. Hunted him till he got killed. I believe that dogs have a great memory. Just watch a dog hunt a place you normally catch hogs at... They will alot of times work areas they have caught hogs from before.