In the GoLion episode "Phantom Space Flowers" this was based upon, the plants actually caused death rather than a prolonged sickness (the one deleted scene that would have made this harder to refute was of one victim falling over his balcony railing when collapsing).
The only time Voltron's lips move to form words (Keith's).
The first time an antagonist called or even mentioned a member of the Voltron Force by name (except Allura - they knew of her before her joining).