It is never too late to start logging your sources. Knowing where you gathered particular details on an ancestor is very important in your research. When evaluating incongruous information, reviewing which source the details are from can help you decide what is more accurate. Another reason to keep track of your sources is so others can verify or follow-up on your research.
Some ways you can keep track of where you found information on your ancestors are:
1. Maintain a log of sources in a notebook or on your genealogy software.
2. Copy the title page of sources you have viewed.
3. Note materials you have searched, but in which you did not find information. It prevents you from repeatedly returning to the same source.