No, yesterday as the previous day, remember this one is also a patchouli, but i don't recall yukkuris having problems by saying tomorrow or yesterday, clearly not counting the days but the basic concepts of morning, afternoon, night, yesterday and tomorrow, they grasp them well.
Eh, yukkuris abstracting events more than a few days old into "yesterday" makes sense to me.
More so than this group being close enough to Deibu's mother for word to spread about what happened yet Deibu never finding out even though something like that would be a major event.
Well consider this, unlike Reimu who remains in the house all the day, the other 3 always leave to hunt and bring food, so i wouldn't be suprised if they were noticed in the middled of the hunt, and either didn't have the heart to tell Reimu if it really is an abstract way to describe the past, or, if it really happened yesterday and today, after coming back from hunting they would had told her, Patchouli was going to tell her before while Reimu was going about "Reimu's mama always said..."