Then five low values from some previous series were reused...the designs were modified to remove service inscriptions like "AIRMAIL" and the dates were also removed from the designs.  These stamps were printed in different colors from their original counterparts.  These were released in December of 1938 and I would love to know more about this series.

Blekhman says they were postally used but are extremely rare in that state.  In unused condition, they are a bit pricey (~150 USD), but easily found.