Consider replacing "event" by "observation". What you really have is a set of observations, and a state that you infer from it. Observations you make may be rel

Consider replacing "event" by "observation". What you really have is a set of observations, and a state that you infer from it. Observations you make may be reliable, but you have no guarantee that you can observe every fact in the problem. For instance, if you're a payment processor in the EU, and a withdrawal was done in the US, you may not have received it yet, so you have an incorrect balance. If a withdrawal is made in the EU, and you add the balance in the event, you will have mixed a perfectly legit observation with something, which is not an observation but an inference, an artifact processed from your incomplete set of observations. Trust is something that changes over time. When your EU platform was implemented, maybe your US platform didn't exist. But the difference between observations and inference will remain true.