Um...different snakes. Different in size, looks, husbandry, and temperment. Basically two different species, well...yeah, that look alike.
For suris and guyanas, they are purer, larger, and have better saddles. The biggest difference is the tails. Their tails are much more red. They are worth more too. They need higher levels of care. Thats BCC
BCI is actually columbian boas, but they get called red tails. Most people don't use the term red tail anymore, and if they do it is assumed it is bcc. But bci is also called red tails for obvious reasons. They are smaller, and a more rugged look. Freckles, dark tails, ect. Pretty big differences.