There should be other ways to obtain the Field notes.

[Herebedragons]

Even if it's a grindy way, it would be nicer to have indeed another way to get the notes... Being stuck with still 1 note left and unable to get it after tens of hours is frustating...
I'd love some king of "field note fragments" kind of way :
On each Skirmishe/Duty where you can get a specific note, you have a chance (higher than the full note) to get a note fragment, and you need <x> fragments of said note to complete it.
Give it 5, 10, 20 fragments required, with a decent drop rate (20-30%) so this is giving those who are spending(wasting sometimes) their time to get that mount a B-route to look into if A-route (full note) just doesn't do the trick

Yes, you have the Duel to get some of them 100%, but come on, not everyone is able to clear it (and being able to try them is time consuming), not to mention the required preparation...

I suggest the fragments thing cause using Coins could be a bit "weird" to trade from the basecamp (like, the guy is selling notes?! Where did you get them !). I know logic has its limit in the game of course, but let's try not to add more "weird logic" than there are atm.

This seems a bit convoluted, but then again making the notes directly exchangeable for clusters would probably be too easy.

I'm going to echo what some have already suggested, but tying some of the notes to duels at all doesn't seem like a good idea in hindsight. Maybe they could have kept the notes to skirmishes and CEs only, with a slightly higher drop rate, and come up with another specific reward for the duels (because apparently the title was not enough).