Thanks to Sledgeweb for the comparison.
In "Greatest Hits", we see Charlie in his flashback standing on a corner, performing an Oasis song when he is interrupted by a sudden downpour. At first look, it seems this is the same scene from Flashes Before Your Eyes. But if so, where is Desmond? On closer inspection, however, it is evident we are witnessing two separate, but independent events. Charlie's shirt is different, he doesn't appear to have the sign, the surrounding buildings are different (although there is a NewsAgent stand in both, the font is different on the two stands).