Music Taco uses the beta label to convey that it may occasionally not find some albums (even if a source site actually has the album). This is rare but preferable to showing the wrong album. I am constantly improving the matching process to make them even rarer and will remove the beta label in the future (I'm not planning to break Gmail's impressive record!).
To be clear, Music Taco works well and can be used to reliably check where is cheapest to buy your music (I use it myself all the time).
Why does Music Taco not find albums sometimes?
The album data from each source is not provided in a standard format. The data is incredibly dirty and for each source the data needs to be extracted, normalised and matched.
Music Taco has a matching engine that handles many of the irregularities between the data sources; this is the core of the Music Taco service. It is constantly being updated as new differences are found. Unfortunately, the length and breadth of these differences between data sources is enormous!
The last thing I want is for you to proceed through to buy from the cheapest site only to find it's not the album you wanted. For this reason, Music Taco errs on the side of caution when matching. When it is not confident about a match it will prefer to not show it, rather that show an album that may not be correct.
The more people that use Music Taco, the more irregularities I can find, and the faster I can improve the matching engine (I am notified whenever an album can't be matched so I can investigate why and update the engine).
Hey, did you tell your friends about Music Taco yet? :)