Mo. Rev. Stat. § 209.309

The board may offer provisional certification to interpreters achieving a minimal level of certification established by the board. A provisional certification is limited to one year; during such year the interpreter must be reevaluated and achieve the next higher level of certification. If an evaluation slot is not available during the term of the provisional license, the interpreter may be granted an extension. A holder of a provisional certification may only be granted one extension.