Hmm. I'm starting to think that after a certain point (SC16), all sectors gain "Dusk Leather" in the "Schematic Material" slot. The last schematic material obtained is Empty Cluster, and that's only been found so far in SC16. Dusk Leather has been found in 17, 18, 19, and 21 so far. Dusk Leather definitely doesn't occupy the "unique crafting" slot (housing/minion stuff) since the other unique materials do appear in 17-21 (Toy Box Schema in 17 and 21, Iron Giant Core in 20). So far, each sector has had a single item in each of the four crafting-related categories (general crafting, unique crafting, FC crafting, schematics), but there are only so many schematic items.

Also, so far, only one sector has dropped more than 2 types of Materia (SC07 with all three Grade 3 crafting materia). All the other sectors only drop two different types (though any that drop a IV can drop the III of that type as well). Each sector also has only 2 types of crystals, with some one-off outliers that might be typos (wind and water crystals are easy to mix up due to Google Doc's autocorrect, and Ice and Water share an icon).

Oddly, exactly zero trips to SC18 have been recorded... We have plenty from 01 to 21, except nothing from 18.