I wasted my last invitation because I waited for the last minute to give it to the new account, I made sure it never happen again by giving it to my friend on the first day after the validation, now I'm hoping that he will pass the validation so I can get the 100% rewards, members should give the invitation as soon as you have one, to maximize your rewards.
I spend my first 40 epochs trying to max out invitation rewards. I was educating, reminding 1 day before validation, reminding 1h before validation ... even begging not to waste my invitation. Nothing helped me to exceed 20% success rate. Now I don't care. I'm not inviting anyone. I just grab unused invitation rewards. Especially now, when price is stable and network is not growing. When price will pump, mining reward will pump too, people will take care about mining more than now so they will care more about not wasting m invitations. Thats when I'll come back to send them.