If a system has been continuously adjusted over time (like ours) we still work from first principles. Even though we have institutional knowledge in the form of people who have worked here for 40 years, it’s often impossible to know the reasoning behind why a change was made. Most ageing code bases contain redundant logic due to some situation in the past which no longer occurs, or a constraint imposed by a dependency which will now be removed.

For example, what was once a file based batch process meant that other processes had to wait and split their processes accordingly. Replace that with an event based system and everything can run contiously and a lot of the restrictions disappear.