Projections were developed right after Super Tuesday on March 1st and will not be changed. See here.
Right after Super Tuesday, Clinton led Sanders by 199 pledged delegates and had won 59.7% of the pledged delegates (vs. 40.3% for Sanders). Since then, Clinton has widened her lead to 326 pledged delegates and leads Sanders 58.1% vs. 41.9% in total pledged delegate %. The model projected a lead of 389 pledged delegates for Clinton at this point, for a 59.6% vs. 40.4% Clinton lead, so the model is slightly over-projecting in favor of Clinton (by +1.5%). Final model projections are +590 pledged delegates and a 57.3% vs. 42.7% win for Clinton. See table and graph below:
How the model “works”:
The model regressed delegates won by Clinton vs. Sanders for primaries on March 1st and before against the “racial makeup” of those states. The resulting regression coefficients are then used to project future primaries based on the “racial makeup” of those future states.