Why specify "1990"? Because Harmony Corruption has been remastered. The 2008 remaster (often included in the Coded Smears and More Uncommon Slurs box set) uses heavy-handed dynamic range compression (DRC) to make it "louder" for iPods. The (Earache MOSH 24) has a far superior dynamic range. A FLAC rip of the original 1990 CD is the holy grail for purists.
When you listen to the album in FLAC, you are hearing it exactly as the CD master intended.