Not sure exactly what you're after, but so far you're at
Year CC ModelMo Mfr Yr Mfr
74 550 K 7 1973
74 550 K 7 1973
75 550 K 11 1974
75 550 K 11 1974
75 550 F 12 1974
75 550 F 1 1975
75 550 F 1 1975
75 550 F 1 1975
76 550 F 3 1975
76 550 F 6 1975
76 550 K 9 1975
76 550 K 12 1975
76 550 K 1 1976
78 550 K 5 1977
78 550 K 9 1977
78 550 K 11 1977
78 550 K 12 1977
With the exception of the June 1975 anomaly, it looks like - from this small sample - they took summers off after 1973.