I think this is just a translation gimmick. In the brazilian official release of One Piece, this Panel reads (translation from portuguese, may not be exactly the same thing):
The glorious age of the great pirates…
...it was a turbulent and heroic age, in which everyone wished the great treasure called One Piece, hidden by Gold Roger, the only man in history known as "the Pirate King". Many pirates raised their flags to fight in several battles and to have their names known... This is this age.
Now, Stephen's script for Volume 1:
The Great Pirate Age - A massive era spent in search of "One Piece," the hidden treasure of the only "Pirate King" in history, Gold Roger.
Countless pirates would hoist their flags and fight to gain recognition… That is this age.