What are the implications when the GIRM is not followed in the celebration of the Mass?
It depends on to what degree the GIRM is ignored. If the congregation stands during the consecration, the consecration remains valid even though the physical stance of the congregation is illicit (against liturgical law). If, however, a layman attempts to consecrate the elements, the consecration is illicit AND invalid.
Fr. Vincent Serpa, O.P.