Yes, it takes some discipline to keep that working. You need to internalize which changes cause ABI breaks, look for them in code reviews, evangelize that culture to new hires that aren't familiar with the rules (which becomes harder over time as people coming up now tend to spend less time learning C), etc.

Which they explicitly prohibit, in fact if you look at how they design the APIs they'll deliberately add reserved members to ensure they hold the space so that it's much harder to break.