Here is one completed board. It is a particularly tricky Mate in 6 (not 7):
The above Mate in 6 begins with 1. b4! and has 2 lines. Similarly, the Mate in 2 has 6 different lines. All lines will give the same extracted answer phrase
Starting with the Mate in 8 on the first letter board, extract the letters corresponding to each White move. This extracted phrase begins with the enumeration of the answer itself and refers to an item of algebraic chess notation