Emperor's Map? (1.8.6)

I've been around the world of ruin, talking to everyone who could be an old man, with no leads regarding the emperor's map I have in my inventory. I've completed the event with Gau's father (who seems to be the main 'old man'), and afterward talked to him with every party member, but still haven't triggered any event related to the emperor's map or gotten him to talk about anything other than waffles.

Is there anything I'm missing to trigger the event? Is there any way I've missed the window? Potential bug?

The map does something?

The map event is disabled if you've already gotten Locke, since the event just tells you where to get Locke.

That seems like a weird end to the event if you have Locke. I feel like you should still receive the information, put it merely points to something you already know. Even if it's "late", it would still be "complete" then.

True. Don't look at me, though, that's pure vanilla coding.

Huh, I don't think I ever actually found the map in vanilla, either. I think I always thought it was an incomplete quest to begin with...