[scrod]

On "eligibility" requirements:

>Note: Music recordings in other formats, lossless files, or audio recordings that are not of songs and non-audio files (even if in MP3 or AAC format) are not eligible for unlimited music space and will count against your Cloud Drive storage space.

I have to wonder if this is simply a TOS issue or if Amazon is actually doing something similar to iTunes Match and creating audio fingerprints of your songs so as to de-duplicate them.