How many different years was the name/designation cetme?
CREATE TABLE "table1_26389588_1" (
  "name_designation" text,
  "year_of_introduction" text,
  "country_of_origin" text,
  "primary_cartridge" text,
  "primary_user" text
);
SELECT COUNT("year_of_introduction") FROM "table1_26389588_1" WHERE "name_designation"='CETME';