Some accounting and documentation problems at Fannie Mae stretch back more than two decades, according to the top regulator of the government-sponsored enterprises, while instances of alleged document tampering stem from questionable accounting policies that provided Fannie executives with maximum bonuses in recent years. Office of Federal Housing Enterprise Oversight Director Armando Falcon presented this disturbing information during a hearing this week of the House Financial Services Subcommittee on Capital Markets, Insurance and GSEs.…