This firm produced perfins from 1930 to 1951.
Here is a PD cover produced in that time:
Used 15 June 1943 to British Guiana
PD perfin on 20¢ airmail definitive (1931) - Scott C7, Edifil 258
PD perfin on ½¢ Victory postal tax stamp (1942) - Scott RA5, Edifil 5
And here are some of the stamps which have PD perfins: