^ Goodbye Happiness still sold over 2 million copies in digital sales, as did most of the older tracks from the compilation. Hikki is a pretty unique musician on the sense that almost all of her singles during her whole career are pretty much huge hits, but I really doubt she has 2 million hardcore fans... I would count the SC2 sales as her core fanbase (as it came with a new EP) and her usual digital sales as her casual listeners.
Even if SC1 had huge sales sales, it also sold way less than any of her previous albums, and this fact itself goes against the usual for the jpop market, where the compilation tend to be the last relevant relese and the overall best selling album. Japanese loves compilations, but this doesn't mean they will buy again a lot of stuff they already have just because it is a compilation. Even more Hikki that is marketed towards adults for longer than Ayu or Namie for example, and adults are less likely to buy something just because there's an idol name on it.
