Apple's advice, frankly, is idiotic.
Yeah, okay, the manufacturer of the device is providing "idiotic" advice on how the use the device they made. Seems legit.
It's impossible to not use 100% of your battery life in one month.
Nothing is impossible. Difficult, maybe. But the advice clearly translates to something very simple: just the the phone and don't worry so much about it.
OP: Keeping the phone on the charger 24/7 for weeks on end, or constantly keeping the battery dead and without a charge so the phone can't even power up, are both extremes that aren't good for the battery, so those are to be avoided if possible. Other than that, you're fine. And sometimes, phone batteries die after 14 months. These things happen.