The OP clearly has more than a clue about the domain.
If you work in a complex domain for any length of time you realise that domains change. I don't just mean that requirements change but the actual real world domain changes.
As it happens, I have been babysitting a large system in this domain since 1996. ISINs were hardly used then, and many types of derivative financial instruments hadn't been invented. Government regulations too keep changing, often bringing into existence completely new data points.
'Knowing a domain' is a meaningless concept in long-lived business system.
Excellent point. This puts some of the comments above about how agile methods could quickly identify these problems and address them by refactoring into doubt. You could build a very big system, understanding the domain well, and then have a regulation change introduce new issues that you could not have anticipated.
Beyond finance, health care would be another setting where this could be important (HIPPA must have caused a lot of hasty alterations).
If you work in a complex domain for any length of time you realise that domains change. I don't just mean that requirements change but the actual real world domain changes.
As it happens, I have been babysitting a large system in this domain since 1996. ISINs were hardly used then, and many types of derivative financial instruments hadn't been invented. Government regulations too keep changing, often bringing into existence completely new data points.
'Knowing a domain' is a meaningless concept in long-lived business system.