Here's a copy of a posting I made sometime ago on the main Greco page that might help put Greco in some proper perspective:

It's believed that Greco's games were fabricated (by Greco) although it can't be proven. I like to think that it doesn't really matter. If he could invent the games, he would be capable of playing the games. Greco traveled extensively throughout Europe, playing, teaching, giving and selling his book (actually manuscripts). He pretty much cleaned up wherever he went, making a small fortune in the process. He beat his own mentor, don Mariano Morano, who was considered the strongest player of that time.

He came up with an idea...to publish games in toto, something that was uncommon at the time - mostly, writers presented positions or problems. After his death, (supposedly from a disease contracted in the New Indies around 1630-1634) his manuscripts were published under a single title by Henry Herringman of London. The translation by Francis Beale was called: "The Royall Game of Chess-Play.
Sometimes The Recreation of the late King, with many of the Nobility. Illustrated with almost an hundred Gambetts. Being the study of Biochimo the famous Italian"

notice the misspelling of his name...

The book became THE classic up until Philidor's book and those of the Modenese writers, Lolli, del Rio and Ponziani.

Copies of Greco's book in those later days were referred to as Calabrians because Greco was from Calabria and was often called Il Calabrese.

Rousseau tells a funny story about trying to improve his chess by spending months all alone in his room, agonizing, trying to memorize his Calabrian, only to find that afterwards he played even worse than before because hardly anyone would ever play the moves he had memorized and even when they did, he got confused and screwed it all up.

Murray called Greco's book, "one of the most important productions in the history of chess."

So, whether the games are fabricated or not seems to me to be insignificant.