Mr. T thinks Shallan's brother could have taught her surgebinding
Already they hypothesized that the girl had been trained. If not by Jasnah, then by the girl's brother, before his death.
If Mr. T is correct either
1 Helaran bonded a spren or
2 Helaran stole an Honorblade
Mr. T told Szeth
"I have learned this only recently. Yes it makes sense now. One of the Honorblades has vanished."
Seth blinked, and he focused on Taravangian, as if returning from a distant place. "One of the other seven?"
"Yes," Taravangian said. "I have heard only hints. Your people are secretive. But yes ... I see, it is one of the two that allow Regrowth. Kholin must have it."
I know Mr. T was intentionally misleading Szeth, but what if an Honorblade really is missing? It's something Szeth could theoretically check on so Mr. T wouldn't want that to be a lie.
I've read other ideas related to number 1. Essentially for 1 to be true, some form of Helaran bonding a spren through getting a weapon than killing said spren would have to be true since upon his death, Amaram was able to bond the sword. If Helaran was a KR with a live spren bonded, killing him would not have left a weapon behind.
If Helaran instead stole an Honorblade, Mr. T could assume he would figure out how to surgebind, but maybe Helaran never realized its potential. Maybe he treated the Honorblade like a regular shardblade.
Somewhat related, I do not think Helaran joined the Skybreakers.
Maize told Shallan
Why did your father join us? Why did your brother seek out the Skybreakers?
I think it's important that he says Lin joined them but Helaran "seeked" the Skybreakers. I think Helaran was looking for answers about who his mom's friend was which led him to the Skybreakers. In his search, he could have found the Shen who some hypothesize are the original Skybreakers or their descendants. I think he tried to kill Amaram either on his own or for a group working against the Sons of Honor.
Sorry if this has already been talked about. I can't figure out how to add the quotes (I'm on an iPad)