Something that has been retrofitted

The act of retrofitting

To add or substitute new parts or components to some device, structure etc., that were not previously available; to modernize

To fix an older version (or older versions) as part of the same process of fixing the newest version; to backport

“The bug was so bad that we had to retrofit our patch to the last three releases, as well as the newest release.”

Of, relating to, or being a retrofit