These printings are from the 1950s, and there are at least three major groups, all easily separated by the changes to BOTH colors. This stamp has several easy-to-spot plate varieties.
Hereis a page
There is a plate variety that is almost impossible to spot
It has a long horizontal scratch to the central design.
Note that the line ends at the denomination box.
This following variety has a long scratch across the palm.
There are other minor scratches to the late issues plate.