I am going back over the Tips and Notes now that I have finished gilding the tree, hoping to pick up more of the subtle details to flesh out my knowledge. In the notes for the Da/De lesson, under Kiom Da, this text appears:
Note that kiom de is never correct, because de never indicates a quantity.
However, four skills later, in the Tips and Notes for the Food lesson, under uses of da and de after the -iom group of correlatives, it includes the following example of a definite quantity:
Kiom de la sandviĉo li manĝas?
Sooo... uhhh. This word never? I do not think it means what you think it means. ;-P
(Seriously, though, that was a misprint in the first lesson, right? Not the second one? While we're at it, how about the examples where -iom is followed by neither da nor de, but instead is used as an adverb modifying another word. Mi sentas min iom malsana. That is also correct... right?)
Yeah, the first explanation is wrong in a global context of the language, not in the specific lesson. You can use “de” after “-om” word. But I hope you can see the difference of the meaning because for me, to give a good explanation of it in English, at least right now, is not possible. XD But anyway just think in the difference of this:
Maro de larmoj. I'm describing of what consists a sea.
Maro da larmoj. I'm speaking about a quantity of tears.
And jes, you can say “iom malsana”.
Examples: How much bread did he eat? - Kiom da pano li manĝis? (We are speaking about a quantity of bread in general)
How much of the bread did he eat? - Kiom de la pano li manĝis? (We are describing of what consists that “how much" he ate) —I'm not sure if the english version of this sentences is right—
They ate as much, as they could. - Ili manĝis tiom, kiom ili povis. (We are not speaking about what they ate)
They are a little bit faster - Ili estas iomete pli rapidaj. (Used as an adverb).
Well, you can check some examples in the Plena Manlibro de Esperanta Gramatiko (PMEG):
http://bertilow.com/pmeg/gramatiko/e-vortecaj_vortetoj/ceteraj/tabelvortoj_om.html http://bertilow.com/pmeg/gramatiko/rolmontriloj/rolvortetoj/de/vorteto.html (look at the bottom) http://bertilow.com/pmeg/gramatiko/kvantaj_vortoj/vortetoj.html