Also, the use of the word 'individual' seems to reinforce it.
If it was only to be one 'living formation' per Spirit Host, removal of 'individual' from the list of applicable units, and adding 'in total' to the end would be a better way of writing it instead.
Example
SPECIAL RULE – The Living Few
Iyanden suffers with a depleted population which has driven them, in times of need, to raising Spirit Warriors to fight in their stead. As a result, Iyanden Craftworld Eldar Armies may not have more Eldar Guardian Warhosts, Aspect Warrior, Ranger, or Windrider Troupes in total than they have Spirit Warrior Warhosts.
But then,
SPECIAL RULE – The Living Few
Iyanden suffers with a depleted population which has driven them, in times of need, to raising Spirit Warriors to fight in their stead. As a result, Iyanden Craftworld Eldar Armies may not have more living formations (Eldar Guardian Warhosts, Aspect Warrior, Ranger, or Windrider Troupes) than they have Spirit Warrior Warhosts.
would maybe be a better way of wording it, if that's it's intent.
Not that I necessarily like the way the rule works. "Hey, guys. We're going to go fight the
Orks. I'll take Harley, Davidson, Honda, Triumph, Yamaha and Suzuki. Sorry Ducati, you can't come. Quota's full. But you 40 Guardians, 30 Aspects, and 40 Scouts can.". Reeks of affirmitive action.

And how come I can take 8 stands of Rangers, but only if I don't seperate them into two groups?
But anyway, I digress. A lot.
Morgan Vening