Read the Sallet's fiend tale here.
What we know from FFX:
• Nearing the summit (Gagazet Mountain Cave), Auron revealed to Yuna that Yunalesca sent fiends their way and "awaits the arrival of the strongest" in Zanarkand. This is where Yuna learned to expect meeting Yunalesca as an unsent.
• This implies that Yunalesca being in Zanarkand is not common knowledge, even among summoners. However, it could have just been Yuna who was in the dark, for narrative purposes.
• If I recall correctly, the game doesn't explicitly mention the fact that Yevon's maesters had knowledge of Yunalesca lingering in Spira, but it was mentioned in the Ultimania. The farthest we got was when Mika candidly asked the group, "You have obtained the Final Aeon from Yunalesca, have you not?"
What we know from the fiend tale:
• He was previously a "monk of Yevon."
• Believing Sin to still be a reality, he says to Yuna, "We must make haste to Zanarkand, to Lady Yunalesca!"
This could mean:
1. That even Yevon monks were privy to such information, implying that it wasn't necessarily a secret, just not common knowledge among Spira's populace.
2. That Sallet may have been a high-ranking monk, thereby granting him access to well-kept knowledge.
3. Either way, it may not have been something that only the maesters knew about.
Well, these are my thoughts. Just wanted somewhere to write them out. I'm not sure how canon these fiend tales are, but I think some of them gave neat insight into Spira's lore.
What we know from FFX:
• Nearing the summit (Gagazet Mountain Cave), Auron revealed to Yuna that Yunalesca sent fiends their way and "awaits the arrival of the strongest" in Zanarkand. This is where Yuna learned to expect meeting Yunalesca as an unsent.
• This implies that Yunalesca being in Zanarkand is not common knowledge, even among summoners. However, it could have just been Yuna who was in the dark, for narrative purposes.
• If I recall correctly, the game doesn't explicitly mention the fact that Yevon's maesters had knowledge of Yunalesca lingering in Spira, but it was mentioned in the Ultimania. The farthest we got was when Mika candidly asked the group, "You have obtained the Final Aeon from Yunalesca, have you not?"
What we know from the fiend tale:
• He was previously a "monk of Yevon."
• Believing Sin to still be a reality, he says to Yuna, "We must make haste to Zanarkand, to Lady Yunalesca!"
This could mean:
1. That even Yevon monks were privy to such information, implying that it wasn't necessarily a secret, just not common knowledge among Spira's populace.
2. That Sallet may have been a high-ranking monk, thereby granting him access to well-kept knowledge.
3. Either way, it may not have been something that only the maesters knew about.
Well, these are my thoughts. Just wanted somewhere to write them out. I'm not sure how canon these fiend tales are, but I think some of them gave neat insight into Spira's lore.