people need to understand the differences between soundscan and riaa certifications....
soundscan deals with albums SOLD....
riaa certifications (ie: gold, platinum, ect.) deals with albums SHIPPED
having said that... here is how the double cd scenario plays out...
Multi-disc albums are counted once for each disc within the album, if the album is 100 minutes or more in total length. For example, each copy of OutKast's Speakerboxxx/The Love Below (total time 134:56) and Shania Twain's Up! (145:44), both double albums, was counted twice, meaning each album was certified diamond after only 5 million copies were shipped; however, each copy of Christina Aguilera's Back to Basics will only count once despite its being a double album, as its total time is only 78:55.
^^^this is for RIAA....
for soundscan it should only scan once since it is a barcode system at POS that is sent to soundscan for them to report