Each employer's base rate for the twelve months commencing January first of any calendar year is determined in accordance with Section 41-31-50 on the basis of his record up to July first of the preceding calendar year, but no employer's base rate is less than two and sixty-four hundredths percent until there have been twenty-four consecutive months of coverage after first becoming liable for contributions under Chapters 27 through 41 of this title. Each employer who completes twenty-four consecutive calendar months of coverage after first becoming liable for contributions under the chapters during the current calendar year shall have a base rate computed at the beginning of the calendar quarter following the calendar quarter during which twenty-four consecutive months of coverage are completed based on the employer's experience through the preceding quarter. The base rate computed in accordance with Section 41-31-50 is applicable for the remainder of the current calendar year. For those employers completing the twenty-four months of coverage during the current calendar year, a new base rate for the succeeding calendar year is determined on the basis of their records through December thirty-first of the current year.