Generally, in civil litigation, there is a two year statute of limitations for filing a lawsuit.* However, there is NO statute of limitations for a licensing board action. This comes as a shock to many health care providers. They believe that if they can make it past two years after an incident, then they are free of any ramifications. States have incredible power and they do not limit their powers with limitations on when they have to take action, so a state licensing board can investigate a licensee within any time frame.
The states do face an issue of staleness in that the more time that passes affects their credibility, it can limit the availability of witnesses and evidence, and it affects a judge's viewpoint on whether the public really needs to be protected by a particular licensee if so much time has passed.
For example: The Texas Board of Nursing is doing criminal background checks and if an undisclosed criminal history is found, the Board opens an investigation to check whether the nurse is a potential harm to the public. There have been several instances where more than two years have passed since the criminal activity and nurses are finding themselves having to defend their license.
*The two year statute of limitations may be extended in several instances (minor, patient did not know of injury etc.).