This column indicates the month (where known) and year that each ROM image was originally released, whether it be to developers, beta testers, or the general public. In most cases, the release date is derived from the compile date of the ROM image, though in some instances (such as the Guardian ROM enhancement) the date was taken from documentation or other trusted sources. If a release timeframe is not known (usually in the case of having no ROM image sample available for study), this is represented with a single question mark in the Released column.