Logging past data?

An OBGYN asked when we started again after my tubal pregnancy (oct 2013) and I couldn't quite remember. I just found my old logs from Jan-June and want to save them on this app so I wouldn't forget again, but haven't found a way to do it. I stated using this in June and I can't log anything previous to that. Does anyone know if it's possible and, if so, how?