Credits to @himitsuru turns out Volume 21 does contain the last 4 Individual Ability Stat

Credits to @himitsuru turns out Volume 21 does contain the last 4 Individual Ability Stat charts!

As a reminder, the Abilities, rated from 0 to 5, starting from the top and going clockwise are:

Physical Ability (体力, includes strength, endurance, stamina, etc.)
Mobility (機動力)
Close Quarters Assassination (近接暗殺)
Long Distance Assassination (遠距離暗殺)
Academic prowess (学力, ie ability to think, learn and acquire knowledge)
Characteristic Skill (固有スキル)

The Characteristic Skill for these 3 are as follows:

25. Yada Touka - B*tch-style Negotiation Techniques
26. Yoshida Taisei - Master of Two Wheels
27. Autonomous Intelligence Fixed Artillery - Transfer Student Combo: Super Mobile Drone
28. Horibe Itona - King of Inventors

Some notes:

For Yoshida’s Skill, keep in mind he’s a vehicle mechanic
Ritsu’s stat distribution are interesting to say the least. It’s neat her Skill is a cooperation-type too, rather than something individual.
The word for Itona’s Skill, 発明王 (King of Inventors), is actually the same nickname the Japanese have for Thomas Edison (not sure of their reasoning though)

And that’s everyone! So nice to have the complete set.