The WRC introduced World Rally Car regulations in 1997, beginning the move away from the older Group A rules. The change allowed manufacturers to build competitive rally cars without producing large numbers of highly specialised road-going homologation versions.
The transition was not an instant disappearance of Group A. In 1997, manufacturers could choose which regulations to use. Ford and Toyota entered World Rally Cars, while Mitsubishi continued with a Group A-based Lancer Evolution. Subaru’s early Impreza WRC programme also retained some Group A characteristics during the transition.
World Rally Car rules permitted extensive modifications to a production-based model, including four-wheel drive, turbocharging, a sequential gearbox, altered suspension and aerodynamic changes. This opened the door to cars such as the Ford Escort WRC, Toyota Corolla WRC and Subaru Impreza WRC.
The wording can cause confusion because Group A cars still competed during 1997. Nevertheless, 1997 is the canonical answer: it was the season when World Rally Car regulations were introduced and began replacing Group A at the championship’s highest level.