I'd say just reverse-engineer it, for those systems without existing descriptive write ups.

For example, say you have a system with a 6.6. This could represent the traditional mainworld or it could instead represent three separate significant settled worlds which - between them - generate 6.6 worth of external trade. The only difference (from the perspective of a ship bringing in consigned cargo) is which of the three jump thresholds they're aiming for . . .