I work in banking in the EU, we process SEPA messages only (not SWIFT) and the standards for interbank communication are very strict and top-down. I.e. (fictional), if you want to charge a fee when you return money after you received an investigation, it MUST be put in "field xyz" and if you do so, "field abc" MUST contain the code "ABC1" or "DEF2" etc.
The times when the standards are expanded or updated are fun (https://www.europeanpaymentscouncil.eu/what-we-do/epc-paymen...), translating hundreds of pages of PDF into working code and then have hundreds of banks implement those changes in the same nightly hour during a weekend...but once it is working, there is no ambiguity or (horror) manual intervention in payment messages. Either you as a bank send valid messages and they are processed, or you don't and they get rejected.
In my experience at the frontlines (banks allowing users to submit SEPA XMLs), the situation is a lot messier. I ended up building an exporter from Xero (globally renowned cloud accounting software) to SEPA for both payments and direct debits, and we have several bespoke export templates for a handful of banks that want it this-not-that way.
The times when the standards are expanded or updated are fun (https://www.europeanpaymentscouncil.eu/what-we-do/epc-paymen...), translating hundreds of pages of PDF into working code and then have hundreds of banks implement those changes in the same nightly hour during a weekend...but once it is working, there is no ambiguity or (horror) manual intervention in payment messages. Either you as a bank send valid messages and they are processed, or you don't and they get rejected.