This firm produced perfins from 1917 to 1948.
Here are three EL SOL covers produced in that time:
Used 26 April 1928 to Matanzas, Cuba
EL/SOL perfin on 2¢ Máximo Gómez definitive (1925) - Scott 275, Edifil 215
Used 1931 (?) within Havana, Cuba
EL/SOL perfin on 2¢ Máximo Gómez rotary press definitive (1930) - Scott 305, Edifil 252
Certified use 8 April 1937 to Montreal, Canada
EL/SOL perfins on two 5¢ Finlay commemoratives (1934) - Scott 320, Edifil 275
Certified use 7 June 1940 to Palmira, Cuba
EL/SOL perfin on 10¢ Tomas Estrada Palma definitive (1930) - Scott 307, Edifil 247
Used 15 October 1940 to Franklin, Virginia, USA
EL/SOL perfin on 1¢ Tobacco commemorative (1939) - Scott 356, Edifil 330
EL/SOL perfin on 2¢ Lions Club commemorative (1939) - Scott 363, Edifil 338
Used 6 December 1941
EL/SOL perfin on 3¢ José de la Luz definitive (1930) - Scott 310, Edifil 253
EL/SOL perfin on 1¢ Tuberculosis Postal Tax Stamp (1941) - Scott RA4, Edifil Sobretasa Postal 4
Used 6 October 1942(?) to New York City
EL/SOL perfin on ½¢ Victory postal tax stamp (1942) - Scott RA5, Edifil 5
EL/SOL perfins on two 10˘ airmail definitives (1931) - Scott C13, Edifil 264
And here are some of the stamps which have EL SOL perfins: