Highest selling 2nd gen boy group album:
TVXQ "Mirotic " (2008) 604k
Highest selling 2nd gen girl group album:
Girls Generation "The Boys" (2011) 464k
These are two of the biggest kpop groups of all time yet neither could reach a million.
These were still great sales. "Mirotic" was the first Korean album to surpass 500k in 4 years since Seo Taiji "7th Issue" (2004).
Second gen was just in a weird spot. Cause 1st and 3rd gen could reach a million easily.