Borderlands 3 tracks zone completion percentages, which you can view on a map-by-map, planet-wide, or galaxy-wide basis. The objectives that make up each map's percentage can be seen in this answer. However, there are several issues that make "100% completion" hard to determine:
- The displayed totals for the challenges on the maps are often incorrect, and you can end up with e.g. "3/2 Fast Travels" or "10/8 Crew Challenges." The discrepancies get even worse when you look at the aggregate totals for a planet or the whole galaxy.
- Some missions, mostly repeatable ones, count toward the map's mission total, but without the mission being tracked in your quest log. The Proving Grounds missions have this issue, for example.
- Some missions count toward your galaxy mission total only, and aren't tracked by any specific map's mission total or in your quest log — namely, the "kill rare spawn" missions.
As a result of all this, my friends and I have reached a galaxy-wide completion percentage of 110%. Is this the highest possible? If not, what is?