For benefit years beginning before the conversion date prescribed in section 75, “base period” means the period of 52 consecutive calendar weeks ending with the day immediately preceding the first day of an individual’s benefit year. For benefit years beginning after the conversion date prescribed in section 75, base period means the first 4 of the last 5 completed calendar quarters before the first day of the individual’s benefit year. However, if an individual has not been paid sufficient wages in the first 4 of the last 5 completed calendar quarters to entitle the individual to establish a benefit year, then base period means the 4 most recent completed calendar quarters before the first day of the individual’s benefit year.