Exceptions or edge cases add additional states.
To fight the explosion of state count (and the intermediate states those generate), you have a couple powerful tools:
1. Identifying and routing out divergent items (aka ensuring items get more similar as they progress through automation)
2. Reunifying divergent paths, instead of building branches
Well-designed automation should look like a funnel, rather than a subway map.If you want to go back and automate a class of work that's being routed out, write a new automation flow explicitly targeting it. Don't try and kludge into into some giant spaghetti monolith that can handle everything.
PS: This also has the side effect of simplifying and concluding discussions about "What should we do in this circumstance?" with other stakeholders. Which for more complex multi-type cases can be never-ending.
PPS: And for god's sake, never target automation of 100% of incoming workload. Ever. Iteratively approach it, but accept reaching it may be impossible.