Complex sentence: When the Pattern system was introduced in 1971 the race was given Group 3 status, and it has been upgraded twice since, to Group 2 in 1987 and to Group 1 in 2004.
Split into simpler sentences: When the Pattern system was introduced in 1971 the race was given Group 3 status. Since then it has been upgraded twice, to Group 2 in 1987 and to Group 1 in 2004.