Comparing a “Best Of” compilation to the original albums will more than likely present a difference in amplitude.  If for no other reason than to provide consistency among the tracks from different sources.

The Asia compilation Then And Now has three tracks from Asia: Only Time Will Tell, Heat Of The Moment, and Wildest Dreams; two tracks from Alpha: Don’t Cry and The Smile Has Left Your Eyes; and one track from Astra: Voice Of America.  The waveform comparison between the original tracks and Then And Now seems to suggest the tracks from Alpha and Astra were boosted to match the levels from the Asia album.

Asia - Then And Now