I think it's sufficient to do the Extents with broad strokes. You SHOULDN'T know exactly what you're going to find as you travel around, even if you're Vargr. The borders given in 1120 can be considered provisional in regard to other eras, and I don't think anyone is supposed to have properly surveyed the area. The IISS would have enough trouble getting good data on the coreward border subsectors, let alone the sectors.
Having said that, the people that live there do need to travel, so the astronomical data needed to Jump is likely gathered and traded, at least locally. After centuries, the Scouts would have some idea, at least as far as stars and mainworld orbits go.
As far as system and world names go, it's likely the same as ever - some attempt to apply local labels, but ultimately the world names are for the use of whoever is using the maps. Imperial star charts use "Lair"; a Vargr one would likely use the Gvegh word their tradition prefers. There's always the option to replace the Gvegh names with a translation. So you might go to "Hellworld" or "Prince Blackmane".