Check kinetics of the ascrobic acid/iodine reaction - if the reaction is slow it is much better to add excess of reagent, wait till equilibrium (15 minutes is often enough) then reverse titrate remaining excess. Think how slowly reacting solution will behave near the endpoint - you add a drop of titrant and you see color change... only to dissapear after several seconds.
If I recall correctly iodometry endpoint is never as sharp as in some other titrations.
End point can be found in both cases - it is either colorless solution getting blue, or blue solution getting colorless. Near endpoint amount of free iodine is so low that solution will be not brown, but - at best - pale yellow.