They are called caudels and if divided, subcaudels.(how I was taught)
Also, its very normal for snakes that normally have subcaudels(divided) to have a number of undivided as well.
There are also colubrid species like Longnose that normally have undivided caudels.
Most Crotalus have caudels, undivided, but also have some divided.
I would imagine your could breed for that trait and see what happens.