I use several 50c-SO stamps for this comparison. These stamps were printed in 1952 on what I think is the second plate. The 1L2 is one of the most common printings-on the regular as well as the 'Servicio Oficial' printings. The master plate varieties are:
1. Clipped V of CENTAVOS.
2. Dot after MAR.
3. Clipped outer line upper left corner.
Here is a pair with the right stamp showing the 'dot after MAR' plate variety.
Here is a detail of this master die variety.
Here is a pair with the left stamp showing the 'dot after MAR' plate variety and the right stamp showing the 'clipped outer line upper left corner' plate variety.
Here is a detail of these master die varieties.
This block has the same plate varieties, but the 'dot after MAR' has a major break to the left outer bar.
Here is a detail of the left outer bar.
