In a recent PEW report, 92% of US citizens have mobile phones. If your not sending notifications to a large portion of these devices we suggest you drive around with a bullhorn and broadcast the message. At least they will eventually get the message, 

Does “better late than never” apply here?

If you have a population of 500,000, then using the PEW report of 92%, that equates to 460,000 persons that have a mobile device. The national average of how current systems gather cell numbers is around 6%. That equates to only 30,000 cell phones being notified.  Using some basic math skills would mean 430,000 people did not receive the message.