Master Evan Piel had split the hyperspace route data in two, giving one half to Admiral of the Navy Wullf Yularen, who had been with him at the time, and keeping the other half on himself. In the end, Evan Piel was killed by Darth Malthael on the Nal Hutta satellite, while Wullf Yularen took the other half back and handed it over to Palpatine.
Master Evan Piel's half of the data was eventually recovered by Anakin Skywalker and turned over to the Jedi Order for archival.
Thus, Palpatine ultimately obtained the complete data and treasured it as one of his greatest trump cards.
In other words, although Tang Xiao knew of the existence of this hyperspace route, he did not know its precise data.
However... the Givin once again proved that they were the finest mathematicians in the Milky Way Galaxy.
What Tang Xiao had actually given them was only a rather vague concept. After all, he merely knew that, in the story, General Grievous had led the Confederacy of Independent Systems' last main fleet—over a thousand warships—in a direct surprise attack on Coruscant, and he also knew the approximate starting and ending points of the route. He knew nothing more detailed.
After all, the story was not really going to spell out the data for a hyperspace route, was it?
Yet the Givin had actually managed to calculate this hyperspace route from such scant information, after a long period of computation!
The Givin's greatest mathematician, Baher Banak, had once again presided over this epic calculation.
Baher Banak had been the chief contributor during the earlier Battle of the Eriadu system, successfully calculating the stellar flare and then calculating how to use it to affect hyperspace routes. Likewise, when the Galactic Republic launched its massive assault on Yago-Dul Planet,