I haven't seen the terms but I believe it is a simple cross currency swap. The problem being less the complexity than the off marketness. I believe that most accounting standards make you realise a loss or a liability if you enter into a significantly off market transaction.
Yes their leg was off-marketed.
At the time, ESA 1995 allowed this kind of transaction (actually most euro countries lobbied for looser rules on swaps as every major treasury was employing CCS (France, Germany and Italy to name a few, at the time those countries were running budget deficits hence they were in no position to argue for fiscal conservatism). Eurostat knew, even if they didn't (which is impossible as those transactions were reported) they could have if they read Risk Magazine.
Also, Goldman was just a piece of the puzzle, most deals were between Greek banks.
Seriously, they did their job, and in fact it' still business as usual (you'd think relationships went sour otherwise)
Apparently Maastracht accounting is not like most accounting.