Where exactly are you seeing this list? From the API? If so, you'd be better off using the image slug instead of the image id. The current image id for CentOS 6.5 x64 is 6372108, but these ids are not guaranteed to be stable. If an image has been updated its ID will change. In this case, there was an update to the image to provide a number of security updates by default. If you make API calls with the image slug (
centos-6-5-x64), that will continue to work even if the ID changes.
Though to answer your direct question, there should be no need to rebuild a droplet that was originally created from an older image.
Hopefully that clears it up, but if I'm miss reading your question, please let me know!