Umm.. I'm not sure you are right when you say high schools dont keep records over 10 years. All schools by law are required to keep every record of every student. In fact you can go and look back into archives as long as 100 years ago and even more.

Recently all student records were digitized so records couldn't be lost due to fire.

Im not sure im understanding your problem correctly. If a school can produce a transcript that shows you attended school from spring 1997 onwards how is she adding the math incorrectly ?