Yes they knew, the entire world knew it! Here is an article from 2004 where Greece was warned, and a 1995 report from NUI Galway. These are just 2 results that came up on a Google search. It is very simple: the Greek can blame whoever they please too except themselfs. But the bottom line is the information was available and when it wasn't an issue in any election over the past decades it remains their own fault for not asking about it. As an example, in my country we take financial policy of our government very seriously, and we've been doing that since "Maria gave birth to Jesus".
To exit this stupid discussion, with an advice to you to educate yourself better i quote the endresult of the 1995 report:
It also means that the undiscounted value of the debt is infinite.
Based on the second result, we conclude that the Greek budget deficits are 'too large'.