EU watchdogs claim they were unaware.
Greece was required to reduce their debt to GDP ratio each year, as a requirement for euro membership. Instead of cutting debt, Greece paid 1.5 billion euros directly and indirectly to hide 2.8 billion of debt. The "missing" debt was lent by Goldman Sachs. That 2.8 billion debt ballooned into a 5.7 billion euro debt.
The use of off-market swaps was "legal" and secret. The use of fictitious exchange rates in the currency swap agreements made Greece's debt appear smaller, creating the false impression that Greece's debt was shrinking.
I thank JSMineset for bringing BBC's video "How Goldman Sachs helped mask Greece's debt" to my attention, and I acknowledge both.