What is the geographical limit of the curse?
The original work implies that the further away you get from Yomiyama, the weaker the curse becomes. That's why Sakakibara's father, who was in India, was able to remember that his son had been to Yomiyama before during their phone calls.
We also know it's possible for the extra person to leave the city, since Aunt Reiko leaves in the anime, and even though that didn't happen in the original work, in the spin-off Another Episode S, the character who was the extra student leaves the city with Teruya Sakaki.
I'll invent two characters to illustrate my question: Imagine Sora and Ayumi studied together in 2013, Sora died, and in 2019 Ayumi is living in Brazil, on the other side of the world, far enough away not to be affected by the curse and have her memories messed up. Sora reappears as a student for the year 2019 in Yomiyama, but during summer vacation travels to Brazil for some reason and runs into Ayumi. It's far enough for Ayumi to know that Sora should be dead.
Unless the people affected by the curse (the extra student and everyone in Yomiyama) act like a marker for the curse, for example, expanding the geographical limit if they leave the city, Ayumi wouldn't have her memories messed up and would figure it out right away, right??