That's a special case. You could have a single bit for special case mode and then very few bits to say what happened. Usually you can encode special states in

That's a special case. You could have a single bit for special case mode and then very few bits to say what happened. Usually you can encode special states in a more compact form because the type of specialness is additional information meaning the single special bit is all you need to grow by. A bloated form for the final state would be a bit to indicate specialness, 7 bits for specialness mode. End state mode is encoded as the turn before plus direction. So adding 10 bits in all, there's almost certainly enough in the knowledge that it is an end state to encode the board in 10 bits fewer, eliminating all expansion except for the specialness bit.