My friend Sacha asked me last week-end how Shazam find the original track.
I was telling that Shazam use a technic that records only specific "points" in the spectral of the original sound. When recording sound, Shazam extract specific "points" in the sound and compare with his database. So only, original can be recognized because the tempo and frequencies must be exact.
Then he answered me, when I tried FrequenZ Oxygene 2 part cover (solo part) with Shazam, the software recognized the original Oxygene 2 !!! LOL.
Didn't you try your covers with Shazam ?