Yes, those are typos. I moved those categories around a bit and forgot to rename.
You mean the internal organization of the “21 Ideas”? (Now renamed to “Ideas and drafts”, see below). At the moment it’s still work in progress (my -perhaps ambitious- goal is not only to use the system from now on but to organize my existing data, at least in the data partition and cloud drive that I currently use, and I have a lot of stuff to organize) but I’m just creating items for individual research ideas. For each idea, what I store there are basically preliminary notes, links to material and drafts (because if the idea ends up being fruitful and I make a publication out of it, then that would go to the Publications category, if I present it somewhere that would go to Presentations, etc.)
I hope this clarifies your question, but otherwise feel free to ask.
By the way, the whole thing has evolved (because as I actually reorganize things, I notice things that I hadn’t noticed before, even thought I gave everything quite a bit of thought). Right now it looks like this:
-
00-09 Meta
- 00 Index
-
10-19 Personal
- 11 Photos and Videos
- 12 (Censored hobby/interest 1)
- 13 (Censored hobby/interest 2)
- 14 Purchases
- 15 Personal and Family Bureaucracy
- 17 Learning
- 18 Creativity
- 19 Events
-
20-29 Research Materials
- 21 Ideas and Drafts
- 22 Datasets
- 23 Experiments
- 24 Bibliography
- 25 Third-Party Research Software
-
30-39 Research Outputs
- 31 Publications
- 31.21 2021 …
- 32 Presentations
- 32.21 2021 …
- 33 Posters
- 34 Reviews/MetaReviews
- 33.21 2021 …
- 35 Software
- 36 Grant Requests
- 31 Publications
-
40-49 Teaching
- 41 Course Materials
- 42 Grades
- 43 Organization (assignment of hours, timetables, etc.)
- 44 BSc/MSc Theses
- 45 PhD Theses
- 46 New Degrees and Curricula
- 48 Teaching Publications
- 49 Teaching Projects
-
50-59 Admin-Bureaucracy
- 51 Certificates
- 52 Promotions
- 53 Evaluations
- 54 Reports and Timesheets
- 55 Misc/Day to Day Admin
- 56 Conference/Event Registrations
- 57 Project Budgeting, Accounting, QA and Misc
- 58 Hiring (Offers and candidates)
- 59 CV
-
60-69 Service / Other academic duties
- 61 Event Organization
- 62 Outgoing Grant Evaluations
- 63 Outgoing Thesis Evaluations
- 64 Outgoing Letters and Certificates (recommendation, etc.)
- 65 Press and Dissemination
- 66 Invited Talks and Other Events
- 67 Academic Societies
- 68 Websites
-
70 Finance
- 71 Banking and Investments
- 72 Property
- 73 Taxes
-
90-99 Miscellaneous
- 91 Travel
I’m using the system close to the limit, as many numbers are close to 10, but I think I won’t overflow 
The pressure of the decimal system is actually great because it forces me to think about logical grouping of things rather than spreading out too much and having flat hierarchies.
By the way, one limitation I’ve come across is that there are things that are in cloud folders shared with other people, and I can’t do much to organize those to my liking. For example, for some courses, there is a folder shared with all the professors that mixes course materials, organization and grades (so it would cut across 3 categories). And for some research projects, there is a folder where people put 54 Reports and Timesheets, 57 Project Budgeting, Accounting, QA and Misc and maybe even the grant request that lead to the project (36 Grant Requests). I can’t really convince everyone to follow my personal organization scheme and, in the case of OneDrive (which we sadly use at my workplace), I think I can’t even move folders around or rename them (in the much saner Dropbox, it’s possible to locally rename or move shared folders without other people being affected).
Any ideas on how to deal with this apart from creating symlinks/shortcuts galore? I guess I can live with it, the perfect is the enemy of the good, but I was wondering if anyone has found a clever trick to improve on this limitation.