Many people lump most Red-Tails into BCC but that is not entirely true. BCC and BCI are usually used when the specific origination lacality is unknown. Here is a simple list of the main groupings of Red-Tail Boas (this is incomplete by the way as some of the sub-species are still being debated regarding their actual status).

Red Tail Boa Constrictor or B.c.sp. for short (comprises the entire group of red-tail boas)
|-Typical Nomenclature- Where they Occur (note there are overlaps in their ranges)
|-BCC- B.c. constrictor (Venezuela, Columbia to S. Brazil)
|-BCA- B.c. amarali (S. Brazil, E. Bolivia, Paraguay
|-BCI-- B.c. imperator (Mexico, Central America, Ecuador)
|-------- B.c. longicuda (Thumbes Province, Peru)
|-------- B.c. melanogaster (Ecuador)
|-------- B.c. nebulosus (Dominica, West Indies)
|-BCO--B.c. occicentalis (Argentina, Paraguay)
|-------- B.c. orophias (Trinidad, St. Lucia,Dominica, St. Kitts)
|-------- B.c. ortonii (Chilette, Peru)
|-------- B.c. sabogae (Tabogo Island, Panama)

The pair I have came from Pete Mimicose. Lots of times you will see references to Bolivians as "Silver Backs". This is really just a means of describing a particular look or trait that a particular bloodline is carrying. I don;t know that these are silver backs. From most of the references to silver backs that I have seen, I would have to say that this pair are not silver backs.
Thanks, Chris

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