Originally Posted by Fat Princess of Johto
There's a moving NPC at the bottom of the Route, so you can't see him when he moves (he's the only one that does). So you can't really tell if you're going to have to resave or not, you're just going to have to hope that he doesn't move. But most of the time, he won't if you're fast enough :)
If he does, just resave like you did this time.
It's also easy if there are roamers left, as you can check if you hit your seed faster, using the roamer method.
Although using elm calls will also let you know if the NPC moved or not. If it moved, then the elm responses might have been skipped by (roamer's advances + NPC advances) frames.
Usually in my experience, the NPC will advance 2 frames sometimes, even if you mash the A button (or the lower right section of the touch screen)