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I know Cambridge/Amazon have every test available, but is it worth to purchase all of the tests? I have 29-38/52-61 as of right now. While I know that there are differences between the earliest tests and the most current ones, what are the differences (noticeable or still worth to practice with) and to what extent should one "subtract/curve" to compare to scores on the more recent tests?

Also, is there a reason, aside from offering them to LSAT prep companies, that certain tests are not sold by the LSAC?

I'm thinking of buying the LR sections from 1-6, but cambridge sells each section for 1.75 each....so 3.50 for the 2 LR sections that are in a test..