oh hell yeah, absolutely. This sort of code is not uncommon at all but is pretty much incomprehensible (let alone maintainable) for anyone beyond the original implementer
Some automatic tools could help (although I doubt thay'll work on DBase III): Static analysis to see what's there, version control to start at the top and log your way through and be able to rollback to a previous working version.
But it's at the very least weeks of pain.