The easiest way to spot these type errors is to look for the same color insert on the end facing an oppposing group of inserts... and compare the middle insert color with the other group(s) of s/s/s inserts.

From left to right ... note the blue insert in the middle at 7;00 o'clock as opposed to green middle inserts on the other two groups. In addition, the center color of one set of inserts is blue as opposed to green center inserts on the other two insert groupings.

Check out the pink insert on the end at 7 o'clock, facing the pink insert at 5 o'clock on the adjacent insert group in the center photo.

In the photo on the right, note the blue insert at 10 p.m. facing the blue insert at 7 p.m. and the pink insert at 2 p.m. facing the pink insert at 5 p.m. ... which is really a double error.

Fascinating stuff!