How much input a buyer gets really sort of depends on the breeder. Some breeders don't really care what you name your puppy as long as it has the breeder's kennel name. Other breeders use themes and let buyers choose their names within a theme. Others name the puppy with no input at all from the buyer.
To see whether a name has been used, pick the least common word in the name and type it into Sally's database, http://pedigrees.zandebasenjis.com
I got my first two dogs from Robyn who uses themes for her litters. Nicky is from the "Time" litter and had named himself before I got him so came to me with call name and matching registered name. Rally is from the "Moon" litter and I had her call name picked before the litter even had a theme so her call name and registered name are unrelated.
When I bred my first litter I decided to use themes but with my first litter, I didn't require a specific word. I had already picked my keeper's name, Sourcery, so went with a magic theme. My other two litters have a common word in the names more like Robyn's themes. They are my Soul litter and my Time litter. I'm not sure you could say L'Ox has a theme but I tell people he is my "Chinese Curse" litter, you know "May you live in Interesting Times."
So it really depends on the breeder.