It is possible to lose a donor if they have to always fill out the form everytime they come to the site to give a donation. If they gave to us once, then why can't the fields repopulate with their information (other than the CC and exp. date) and they update whatever is needed This saves them time and they appreciate
The only way this could happen is if you gave the donor a unique code that they could type in and the information could be pulled onto the form. That or you would need to force them to log in so that you knew it was them and not someone else. You would not want the form to just remember information when it thought it saw the same donor again. It would be a security nightmare if that was ever wrong. So , it really comes down to the security of information regarding the donor.