Impossible positions in tablebases. For what are they?

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keymasta
 
Black King i double check, and black Bishop on h8 blocked with black pawn? This one and other impossible positions exists in tablebases
 
3NB2b/6p1/2k5/8/4K3/8/8/8 b - - 0 1
Martin_Stahl

The double check is certainly possible. d8=N+ and if it is a 960 game, the rest is also possible.

 

But I don't think the tablebases are as interested in how legal the positions are just what that material combination is and whether it is a draw or mate for one side and how many moves.