The block fits together IF one uses 1/4 inch seams.
The unfinished size (when using 1/4 inch seams) is 12 x 12 inches.
The finished size (when using 1/4 inch seams) is 11.5 x 11.5 inches.
To make it "work" using 1/2 inch seams:
Original size ->> new size
5 x 5 ->> 5.5 x 5.5
5 x 4 ->> 5.5 x 4.5
8.5 x 4 ->> 9 x 4.5 (cut 2)
12 x 4 ->> 12.5 x 4.5