How could a map show Pacific Ocean before it was discovered?

I read a news report on the Internet today about a map made by a German monk shortly after Columbus discovered America....but the map showed the Americas, completely, with the Pacific....and it hadn't been officially discovered! How do you explain this? Could there have been earlier discoveries not widely known?
Balboa didn't discover the Pacific until 1513; this map was made in 1494!

Firstly is would recommend that you use your common senses on questions like these, this is what defines you as a smart person. A man called Ballboa had crossed the isthmus of Panama and discovered the pacific. Clearly, someone must of have seen it for it to be on the map.

An idea was that the date was changed to make the Monk famous or to be recorded in history???

-Welshdragon*

You have to realize that many of the discoveries made in the 1400's are still a mystery because in those days secrecy was essential. This specially applies to the portuguese explorations. The portuguese were the first europeans to explore the open Atlantic in the very early 1400's, almost 100 years before the spanish.

In the 1420's Portugal had allready disvovered the islands of the Azores, now part of Portugal, and they are almost in the middle between Europe and the americas. Many historians agree that probably Portugal already knew there were lands to the west because they were sailing across the open Atlantic for almost 70 years before Columbus.
For example in 1474 the portuguese explorer Joao Corte-Real was rewarded by the king with lands in the Azores for having discovered "the new lands of the country of cods", most probably today's Newfoundland and Labrador, since in 1500, 1501 and 1502 both his sons, Gaspar and Miguel where the official "discoverers" of Newfoundland and Labrador.

Curiously enough, Labrador was already known and called that way because in 1448, 50 years before Columbus, a portuguese explorer Joao Fernandes Lavrador sighted the enormous landmass, supposedly went ashore and realize it was either a massive island or a new continent.

Many historians say that that was the real reason why the portuguese king refused Columbus proposal of sailing westward to find a faster route to China and India, because he not only already knew that to the west you would reach a great mass of land that was not China nor India and especially because in 1488, 3 years before Columbus's voyage, the portuguese explorer Bartolomeu Dias sailed around Africa opening the sea route to India, the real on, fastest and more lucrative. What's strange is that since Columbus knew about this, since the portuguese king Joao II suspected there was a continent to the west, why did columbus insisted in leading the spanish to the west? One of the reasons was that he was a portuguese secret agent that was to "entertain" the spanish with the new lands to the west (that had no gold or spices, the spanish didn't make money from the americas untill the 1540's) and leave the portuguese alone with the multimillions sea route around Africa to India and China. Later events proved the portuguese were right, i the 1540's when finally spain managed to get some gold out of the americas, the portuguese had built and Empire, controlling all of Africa, the Persian Gulf, India, China, Malaysia, Indonesia and even Japan.

So it's not a great surprise that someday all these facts are definitely proven, but that map and others that have appeared are hard to date and are most probably either fakes or maps from the mid 1500's wrongly dated.