My introduction to fungible was in a New Yorker cartoon, with a partner (at a law firm chastizing a clerk) and explaining, "Partners are forever, clerks are fungible!*" or something to that effect--

Ann Rule use the word to, in one of her books about a mother who had Munchousen by proxie, and would kill her childern as they reached the age of 2 or so (she had 3 different husbands, and lived in several different small towns, and in 15 years, had something like 10 children, all who die of 'sudden infants death syndrom'... and Ann Rule use the word to define the mothers attitude to her children... they were fungible... and used to gain sympathy for her self...

i think it can be used beyond grain and commodities, and yes, international brokers are fungible...