35 Miss. Code R. § 10-01-203
If there is no construction or expansion of a facility, the expansion in labor forces must take place by the end of the following tax year for the certification and county designation to remain valid. If there is a construction or expansion of a facility, it must begin within one (1) year of the certification for the certification and county designation to remain valid. This initial certification is only good for the credits covered under the specific certification generated during years two (2) through six (6) after the expansion of labor. This certification to lock in the county's classification will not be granted retroactively. For subsequent qualification and credit for additional increases in employment, the county designation in effect at that time should be used to determine the qualification and amount of the credit.
35 Miss. Code. R. § 10-01-203