Yup they're just "estimates" . The test makers are the only ones who know how exactly the raw scores convert to your overall score .
For instance you can get a 710 either with a Q50,V35 /Q46,V42 /Q49,38 /Q 51,V34 ( these are just some combinations , I'd imagine there are quite a few combinations that can lead to the same score ) .
Actually how it works is each Raw score isn't the same . For example say two people score a 50 in quant , one person might be in the "high end" of the 50 and the other might be on the "low end" of the 50 . So what that means is eventhough their score reports might say they had the same score in quant , the CAT algorithm will give a higher value to the guy who's at the higher end ( all this is done internally ) . Again , none of us know exactly how this conversion is done , only the test makers know about this .