You think you need X amount of transport and suddenly, you realize you really need Y and Z plus support from ABC.
It takes doing it to figure out where the flaws are...and each city and town is different.
Different people, needs etc. Timing etc. You move too soon and you may kill people who would've lived otherwise (like vent patients, bed-bound etc).
It's easy to play God (not you) but unless you've been in an evac situation, where people were dying, its a bad place I wouldn't wish on my worst enemy.
So you only get 80,000 people out when you needed transport for 100,000.
That's still 80,000 people out of harm's way. You cannot let the possibility of partial failure prevent you from even trying. Unfortunately, that's the mantra of too many governments nowadays.