It’s not that easy… There’s a bunch of proprietary systems, each adapted to dozens of specific regulations.
Id say every 200 lines or so of code you make a mistake. Sometimes you hit the wrong key, sometimes you have a brain fart, sometimes there’s some complex interplay that leads to occasional issues.
A good programmer catches like 90% of them. Giving time for self-testing catches another few percent. A rock solid design with high automated test coverage might cut mistakes by a factor of 10. Add in great qa (a low paid role with low status and easily cut for profit) and you might get 90% of whatever is left
There’s no perfect code, and if you have to interface with another company jealously guarding their own implementation? They might give you a sample file and a short format definition. Is it correct? Can everyone read the spec and come away with the same understanding? Is there room for a bad actor to put their finger on the scales?
It’s just beyond human capability to write perfect code, even in the perfect environment. And the ideal solution is redundancy - ideally you’d have like 5 teams running very different software in parallel for each vote and count, and you’d debug any situation where they don’t all agree and recount.
But that would be ungodly expensive and politically impossible… There’s room to do better, but there’s no money in it