A lot of our old books are the original manuscripts from libraries, archives, and private collections that we have digital scans of (that I end up printing out). The modern printed editions often try to "improve" on the originals through ease of use (modernising clefs and notation) through to interpretation suggestions... often leading to scores that bear very little resemblence to the originals... and with a huge loss in information due to the lack of expertise in interpreting historical markings (many of the symbols are the same, but the meanings are completely different!).