I upvoted you, because I had the exact same question, but I also wanted to comment. It seems SOOO common, especially for technical writers, to overuse, or invent, acronyms and to expect that people automatically know what they are talking about. I've been in software for about 20 years, I'm very familiar with the concepts around backwards compatibility, but I have never seen it abbreviated 'BC' before.

If you want to use uncommon acronyms, please be sure to spell it out (e.g. "backwards compatibility (BC)") the first time you mention it.