[ColinDabritz]

This threw me off for a bit.

The \1 is from the original puzzle, and refers to the value of the first (capture group). I ran into this issue while filling out the puzzle. The \1 is required to 'propagate' the value in that square to other places. The puzzle is ambiguous without this fix.

Thanks for the pointer, I've added the note in the comments. Hopefully the puzzle is editable.

Lovely puzzle, and it's a great quote. :)