English to Spanish Other Law (general)

"For porpuses of determing the benefits payable pursuant to clause(a),the value of the Restricted Stock Rights or Restricted Shares, shall be based on the price for Shares of Aviall,Inc.common stock fixed by the Board of Directors of Aviall,Inc.for porpuses of calculating the number of shares of Restricted Stock Shares to be awarded to the Participant, and such value shall be included in "Basic Compensation" for the year in which such Restricted Stock Rights or Restricted Shares,was awarded, but only to the extent such Restricted Stock Rights or Restricted Shares,VESTS.

Estoy intentando traducir esta oración pero no logro entender a que se refiere el último verbo("vests".¿Hace referencia a "the value of the Restricted Stock Rights or Restricted Shares"?
Es una oración muy larga y muy confusa.Espero que puedan echarme una mano.Gracias!