Complex sentence: By 2005,1,165 people had settled Son of BOSS cases with the IRS; but the complex structures used in the schemes were hard for the IRS to unravel, and it was losing some court challenges to its crackdown.
Split into simpler sentences: By 2005,1,165 people had settled Son of BOSS cases with the IRS. The complex structures used in the schemes were difficult, however, for the IRS to unravel, and the IRS was losing some court challenges to its crackdown.