The notes to the Code clearly state that it is not intended to be applied retroactively to existing buildings provided:

• The building met the Code at the time of construction
• Existing nonconformities do not create an immediate threat to life safety, 
• The work does not increase the level of nonconformity and   
• All new work must meet the current edition of the Code.

Typically, it is advantageous to provide some form of improvement to existing nonconformities, but addressing existing nonconformities can be tricky to navigate as it may require significant work or reconstruction which may not be practical.  Additionally, upgrades may be triggered based on the scope of work, dollar value or size of the project. In some cases, if the project is large enough, upgrades to energy, seismic restraints, exiting, fire protection (sprinkler protection) and accessibility can be asked for by the Authority Having Jurisdiction (AHJ). This can lead to unexpected costs to the project, or the project may not go forward at all.