Fannie Mae’s and Freddie Mac’s historical dominance of the mortgage-backed securities market officially came to an end in 2004 as new data from the government-sponsored enterprises reveals that the GSE share of total MBS issuance plunged to just 47.4 percent last year. That was way down from the commanding 70.7 percent MBS market share that Fannie and Freddie held as recently as 2003 when the two GSEs combined for a record $1.92 trillion in MBS…