Data field not populating correct info

I am in the Army and have an excel sheet that we use to show the status of our helicopters. I have 5 tabs on the excel form and most tabs pull info from the back tab which I cut and paste new data in every morning. On the phaseflow tab K 2-18 shows incorrect data. I put a forumla in there to take the aircraft tail number from the info tab according to the sort function. This worked perfectly for the last year. The other day when I opened it up the cells had the forumla displayed, but not the aircraft serial number. I know a decent amount about excel, but cannot figure out what is causing this issue. Any help in figuring this out would be greatly appreciated. This report goes to the big boss man on a daily basis, and I am frustrated that the report is not showing the proper data.