In the course of poking around, it looks like Ritter always held the view that the sanctions weren't useful.
But that's a different issue than his complete, 180 degree flipflop on whether or not Iraq continued to misreport its WMD.
On that point, he went from saying they were lying, to saying they were not "accounting" properly, to saying flat out that they have nothing.
That last step happened between December 1998 and March 1999.