Prospectivity in criminal law exceptions

Expungement in the United States is a process which varies across jurisdictions.
Many states allow for criminal records to be sealed or expunged, although laws vary by state.
Some states do not permit expungement, or allow expungement under very limited circumstances.
In general, once sealed or expunged, all records of an arrest and of any subsequent court proceedings are removed from the public record, and the individual may legally deny or fail to acknowledge ever having been arrested for or charged with any crime which has been expunged.