There are 2 critical errors in the collected data, which made it hard for me to figure out the correct thing.

Sector 136 (F) is discovered via 135 (E)
Sector 137 (G) is discovered via 134 (D)

This information is displayed partly correct on another website, and even there it is partly wrong.
I wasted weeks farming F for discovering G but nothing happened, so I changed routes and D did the magic trick.