This isn't an error, but you might consider explaining about ケ standing for 箇 and having the pronunciation か or が when you introduce it in 十ヶ月間. I know I was like "wtf is that small ケ that's pronounced か doing there" when I first saw it.
This was actually in the old version of Kanji Damage, but it looks like it's been taken off of the new one. I agree that this one should be back on the list even though we never see it, just because it's the origin of ヶ, the same as learning both 歳 and 才. Here it is if you'd like to see it:
箇 - itemized list
音：KA - the overpaid rapper listed all his CARS.
bamboo (竹) +hard (固)
Early merchants would carve lists of their inventory into scraps of hard bamboo.
箇条：かじょう： an itemized list. wow, exciting! tell me more! (NP)(*)
sometimes you'll see this kanji next to a regular noun, to indicate that that noun is an item on the list.
The most famous example of this is, 3箇月： meaning, 'the third month on the list,' or, as most of us would say, 'March.' although, 99% of the time it's spelled like this : 三ヶ月. Which is good news, because you don't have to use the kanji. but bad news because - although they simplified 箇 into the katakana KE (ケ）, they continue to pronounce it "KA" like the original 箇 kanji. what the fuck??? Seriously, even for Japanese that is retarded.
箇所：かしょ: a place. Not only a physical place - say, Paris or Leningrad - but a place or spot or rank on an itemized list. yeah.(*)
筒 - tube (hitler)
管 - pipe (crown)
箇：itemized list (hard)
The king with his CROWN smokes a pipe of hash, but the tube. sticks out of HITLER's moustache.
It's HARD to list all my vast stash of cash.
edit: I just noticed that this says that ３ヶ月 means "March," which it totally does not.