figure it out the value of each position on its own, without any help or target value.

One way that’s been done before is that the “target” is winning the game – i.e. board positions from each game are labeled by whether or not they resulted in a win. There’s an explanation here, which used a database of 640,000 actual games to train their evaluation function:

  
      cs.tau.ac.il
  
  
    
deepchess.pdf 3

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