Originally Posted by QuiltE

I think you are right KatieMar!
Great Sherlock Holmes'ing!!!!

I don't think there are any extra rows, as QuiltnNan suggests.
Only that the alternate blocks are done in reverse colour/fabric placement.

Whereas Quilterdale's photo has every block (group of four smaller blocks) the same
and when they come together, that incredible secondary pattern shows up.

Does anyone agree with me?