Well, someone on her campaign staff is smart.
These flyers she sent out have the wrong date printed on them, but that has been scratched out and the correct date HANDWRITTEN in.
So, now those who receive the flyer will take closer notice, due to the date being scratched out. They will more likely remember the new date better, due to the attention brought to it.
When the flyers are returned, the HRC staff can call each one, and they have the ‘mistake’ that gives the common ground for discussion, and closeness.
Anyway, messing up the date and providing a correction before mailing it out (instead of having them reprinted properly) is a trick to draw the reader’s attention to the date, and get them to respond better.
Psychologically I know you are correct.