Very few versions of Erasmas survived the trip over the pole
After Erasmas crosses the pole, he describes himself like this:
Standing out there on the street I felt stretched thin, diluted, as if that pale arctic sunlight could shine right through me and give my heart a sunburn.
(part 7, FERAL, Allswell)
This is really similar to a passage in Rise and Fall of D. O. D. O. where someone is getting eliminated from versions of history.
A few paragraphs later, he talks about how he has been harrowed. Harrowing is when you remove the weeds from the soil and loosen the dirt to encourage growth of the remaining plants.
This is what happens to Erasmas after he went over the pole: most versions of him died. The "weed" versions of him didn't survive, allowing the remaining versions to grow, to forge connections with Narratives they were similar to, instead of the other versions.
This is metaphorically similar to Diax's Rake - to "rake away" the Narratives to which we're loosely connected, allowing us to forge new connections to more useful Narratives.
Jad is the one who sent him over the pole. Was this part of his plan - to forcibly harrow Erasmas?
"Let's buy a sextant, then," suggested Fraa Jad.
"Those have not been made in four thousand years," I told him.
"Let's build one then."
"I have no idea of all the parts and whatnot that go into a sextant."
He found this amusing. "Neither do I. I was assuming we would design it from first principles."
"Yeah!" snorted Barb. "It's just geometry, Raz!"
"In the present age, this continent is covered by a dense network of hard-surfaced roads replete with signs and other navigational aids," I announced.
"Oh," said Fraa Jad.
"Between that and this"—I waved the cartabla—"we can find our way to Saunt Tredegarh without having to design a sextant from first principles."
(part 6, PEREGRIN, Peregrin)
This discussion is really a discussion about their underlying worldviews. Jad navigates on his own. His strategy is like Yul's stove strategy: it's imperfect, but it's comprehensible. Most importantly, it's independent.
Erasmas here is reliant on others. He is dependent on other people to say how to get somewhere. He obeys the signs; he is dependent.
Later, Jad tells him to go north, over the pole. There are no signs; he'll have to figure it out on his own. He'll have to display some adaptability.
The versions of Erasmas that survive the trip over the pole are the versions capable of doing this. Most didn't survive, but the ones that did took root, forged connections to similar Narratives, and thrived.