your right, bolivian boas are extremely variable... this is due to Bolivia being right in the middle of south america. it is probably the country with the widest variety of climates in south america. Boa Constrictor C. probably blends in with B. C. Amarali in the north (departments of Pando and Beni) and the amarali probably blends in with the occidentallis in the south bordering Argentina (department of Tarija). this gives us an extremely high variability in our boas, including size, color and paterns...
the yellow female you ask of, unfortunately I dont have info on its specific origin. I do know that boas from the area in Santa Cruz are mostly dark brown and completely pattern like the large female i show and like the large female you own. but you dont have to travel far from the city to start noticing diferences in boas. travel 45 km. north to Portachuelo for example (1 hour drive) and you begin to notice changes... and similar way in diferent direccions.
I did recieve a very large female last year that had a bad respiratory infeccion (around 8.5 ft) she was very yellow in color just like my small female but she had a complete pattern and no peaks. dispite my efforts she died. the owner was a local witch doctor that sold natural medicine made of boa guts (he claimed) to enhance penes size... LOL! he used the poor animal to resemble the sizes his medicins could achieve... LOL
he said he had cought her in Puerto Suarez, this is on the border with Brazil way east of Santa Cruz in the Pantanal area. I past through Puerto Suarez last year and observed that the vegetation was a bit different with a lot of yellow tall grass which gave the land vew a more yellow tone. perhaps boas are lighter in color in these areas because of this.
So to conclude, based on color, the small female could originate from somewhere east as you say!

but i cant explain the incomplete pattern, do you know of boas that come from north east of santa cruz? she had a sibbling that had only a complete stripe from head to tail!! beautiful!! that my cousin kept. my cousin had the whole litter donated to him by the zoo because they didnt have space enough. the zoo probaly had recieved a gravid female that gave birth to these. this was long ago.... we were little kids and didnt know a thing about boas, other than that we liked them lol... the only two left are the pair of yellows i have.
i will post pictures of all my snakes and tell you where each one is from (the ones i know).
I sent you an email some time ago. maybe 6 months ago. i dont know if you recieved it. it had a word document attached to it with discriptions, pictures of boas and nature here in santa cruz, and some questions regarding the breeding of these animals along with it. its pretty interesting i think. I still have it saved, so let me know and I´ll email it to you