The way I see it, I believe that Namine communicated with Terra before Sora went to The End of The World. Namine may have been well aware of everyone connected to Sora before she was even given physical form.
While the point in RoL-time when the scene of the concert happens might be truly around just before End of the World, in some form NaminÃ© must have either future knowledge or be time traveling from the time beyond CoM since as Audo pointed out, she addresses Terra as being the "only one the people of the current time have no idea where he could be", which is a piece of information a just born/pre-CoM NaminÃ© simply can't have even with memory powers as there are no memories that pertain to this fact yet.
By the time 0.2 (which takes place most likely parallel to the last third of KH 1 as far as they have shown) is happening, "the people of the current time" do not only have no idea where Terra is, by that time they also have also no idea about Ventus and if the whole "Terra contacting Aqua"-stuff takes place before Mickey runs into her they also don't know about Aqua either.
The part of Terra being the only
one they have not even a hint towards makes only sense from a post-CoM point in time if not even a post-Re:Coded point as it was during Re: Coded (by first seeing Roxas' appearance and being told of the "very special bond" between Sora and Ventus by Data-NaminÃ©) that Mickey finally learned a hint as to where Ventus might be.
He even outright says that in the first secret ending of Re: Coded to Yen Sid, that they might finally
have a clue towards where Ventus' heart is.
So there is definitely a discrepancy in terms of the timeline that can be arguably resolved only in two ways:
Either a) NaminÃ©'s heart is somehow time-travelling and goes back with present (post-CoM/possibly even post-Re:Coded) knowledge to the time of the last third of KH 1, stirring the Lingering Will somehow and resulting in Terra's essence taking up action or
b) 0.2 covers more RoL-time than what has been hinted at so far (time flow in the RoD is severely warped anyways) and both the Lingering Will/NaminÃ©-meeting and Terra contacting Aqua takes place parallel to later events in the RoL-timeline.
Possibility b) might sound to some more unlikely due to the assumption that Enchanted Dominion (where the particular scene seems to take place) could only be traversed by Aqua before the end of KH 1 due to it being restored afterwards...but that does NOT have to be the case actually.
What if Enchanted Dominion is one of the worlds NOT restored at the end of KH 1 but which fell into the Realm of Sleep instead? We never see or have any mention about ED in titles after KH 1 and Maleficent is constantly on the lookout for a new base of operations, something she wouldn't need to do if ED was restored as then she could use the Forbidden Mountain as a base again.
Enchanted Dominion being still a sleeping world even after DDD (it was never specified that Riku's and Sora's opening of the seven sleeping keyholes actually released all
sleeping worlds) would also allow for some possible connections to a certain other version of ED which we saw in a certain secret ending of a certain browser-game.