[lxgr]

Yes, definitely always include the number of digits, but at your system boundary you still have to pray that whoever you're working with isn't silently dropping that number and re-deriving it from their own, almost-4217-compliant currency database.

Redundancy can be great, but it's not a panacea, since it's not guaranteed to be used in an optimal way.

[jyounker]

How you expose you present your data to third parties is not how you represent it internally.

[lxgr]

Ideally it’s not, but I’ve seen it leak so often that I’d rather be safe than sorry.