[oselhn]

I worked on huge old codebase. Mostly int return values were used as error indicator. But there were at least 3 non-compatible error enums (OK/ERR, PROCESSED/UNKNOWN/ERR, 1/0). Those enums partially used the same int values so you had to make sure to not mix them up (as you pointed documentation was frequently incorrect). Usually it took me several hours to check that error handling in some function is consistent or determine which of those enums is used. You can make huge mess with explicit error handling too.