If a CD is not yet in the AccurateRip DB, the program has nothing to compare your rip against - to be sure your rip was 'perfect' after the first run through.
So it re-rips it several times (this is configurable) and compares the result to each of the previous times. If they a certain number match than this is considered a 'good' result and your results are then occasionally (or can be forced) uploaded to the online DB for the community to share.
The biggest issue with all of this business is there are different pressings, manufacturers depending on country of origin, etc. I guarantee an original pressing of a CD from 1985, of say 'U2', will be different than one purchased today. Manufacturing has MANY variables. Now add in 'remasters', 'special editions', etc. and...so it's just a crazy mess.
So just because your CD is 'the same' as a friends, doesn't mean it is
The Audioholic