I've written this before when people bring up the subject of finding / owning true red tails, or true BCC....
30-40 years ago it was easy to find BCC and BCI (as it was then before commons were predesignated BI). The traits of a BCC, such as the bat wing markings, colouration, and more importantly the scale counts clearly identified the difference between the two. Also everything was pretty much natural colouration and patterning, and you could get some really cracking deep port red or letterbox red tails.
The main issue people had was true BCC tended to grow larger than common BCIs and whilst still attractive lacked the cleaner defined and colourful markings of BCC, so people started to cross them in a bid to get the traits of BCC in a BCI package. However what tended to happen was that you then got BCC with traits from BCI as well. Then people started doing the same with the smaller island sub-species, the idea that a small 5' hog island or clay's boa that looked like a miniature red tail would be so appealing that it made sense to do so... but then the gene pool became really messed up.
As you know, morphs have dominated the past two decades, and traits such as speckling, moustaches marking, crucifix markings, have all been altered through selective breeding of various morph and bloodlines. Now you can get a boa that has a nice clean belly with no speckling, no cross on its head, bat wing saddles all down its back, bright white lining of deep wine red triangles on its tail. The scale count is neither BI or BCI.... (the difference used to be a good 20 or more between them).
scale counts - 75 to 95 dorsal rows.
227 to 250 ventrals.
49 to 62 subcaudals.
scale counts - 56 to 79 dorsal rows.
225 to 253 ventrals.
47 to 65 subcaudals.
However, it's also been proven that some regional BCC's don't always exhibit some of the original traits such as the bat wing / widow spikes. Ian Kerr is a forum member who has a stunning collection of boa's, with know bloodlines. Here is an image of a Peruvian red tail
Not a bat wing in sight......
Andy (user name brothrops ) gives a further example
But just to show how selective breeding (and possible crossing to get the traits) have a look at this image found on a google search
No crucifix on the head, no "eyebrow" markings on the head, virtually no saddles to speak of, no speckling, very clean salmon body, and brilliant red tail markings on a bright white background..... so diverse from the BCC's that were offered for sale a various reptile shows back in the 90's
If you want something that is a true BCC, with a know bloodline then drop Ian or Andy a PM as see if they have any breeding projects in the pipeline, or if not, I'm sure they could put you in the right direction