Bought a kit at a quilt show for a flannel baby quilt. When I prewashed/preshrunk the flannel (8 fq's), some of them shrunk so much they became parallelagrams, impossible to square up without losing a lot of cutting area! Had to piece, which really showed on some of the pieces.
They know that flannel needs to be preshrunk and included a bit more of each piece to allow for that.