IBC stands for International Building Code, and the date (i.e. 2024) refers to the year the code was generated. After adopting the new code, building departments will usually require the new permit buildout be done under the new or current code they have accepted (with amendments) and applied to the plans being submitted. They will also want to know what code the building was originally built under to ensure that the remodel is compatible, and they may require retrofit of certain elements.
Some structures cannot be improved under the current IBC, which can be extremely stringent in its requirements.
The IEBC is the International EXISTING Building code and allows for repairs, remodels, and other changes to an existing structure when that structure is too old to update or to meet current standards. In these cases, the jurisdiction may have decided to allow some improvements under their currently adopted IEBC in order to avoid destroying older buildings or to encourage the reuse of existing structures. Not all structures will qualify for this in all jurisdictions, and review of the code restrictions in the applicable jurisdiction should be done prior to attempting to use it on a project.
By visiting the IBC/ IEBC website for whichever code year applies in your jurisdiction you can find out what types of projects are affected and how this accommodation is applied in your jurisdiction.
Why does permit require their approved electrician?