In a reversal, the Education Department will now reprocess student aid applications that were affected by a recent calculation error and issues with incorrect tax data. The decision, announced Thursday, will affect roughly 20 percent of the 6.6 million applications processed thus far and could further delay when affected students hear from colleges about their financial aid eligibility. The department had previously only planned to reprocess the Institutional Student Information Records, or ISIRs, when students would receive less financial aid because of the error, which was about 5 percent of the processed applications. Colleges use the ISIRs to determine aid eligibility and to package financial aid awards.