sd └── Nintendo ├── Album ├── Contents └── save
All files stored under the Contents sub-directories and save/ use the NAX0 format.
Contains the screenshots: "YYYY/MM/DD/<hex>.jpg". These contain some sort of MAC, the system will display an error for screenshots with invalid MACs.
Contains system-only savedata "8000000000000000" and "8000000000000124".
It seems this directory didn't exist until 2.0.0.
Contains directories "placehld" and "registered".
Also contains file "private". Modifying this file results in the system throwing the <this microSD is for another system> error.
placehld and registered
"placehld" and "registered" are the same, except that the former stores the temp data during eShop title download, while the latter is for the final title data. The contents of the former for a title("placehld/<hex>/") are moved into the latter when title download finishes.
Some of the "placehld/<hex>" directories are temp-only and don't get moved into "registered". These are deleted when the title is launched(?), at that point the directories are already empty.
No titleIDs are stored in any directories/filenames here.
All hex IDs(below XXXXXXXX and NcaId) used here are unique per title/content, these are the same for different systems for the same title(s).
<sub-directory under Contents> └── <directories with upper-case hex: XXXXXXXX> └── <lowercase hex NcaId>.nca └── 00 (Actual file for data storage)