I don't know about Pronto, but the basic most obvious difference is the BGCT follows the 1963 BF&M and the SBC follows the 2000 BF&M. I am sure the differences have been discussed here before. A search would probably give you a good idea about what folks think about the differences.
I'm sure the website is just giving a shorter version of the detailed statement that the prof's and admin have to agree to.
"Without error" where, in the translations we have now, the manuscripts, the originals? This topic alone could be pages and pages of reading on a website designed for the most part, to give basic information to interested students.