1978-09-06 /AP-4172F-BM/01/3a-sources/tops20.rel 1978-09-06 /BB-4170G-SM/01/sources/tops20.rel 1980-02-20 /BB-4172G-BM/01/4-sources/tops20.rel 1983-04-05 /BB-4172H-BM/01/4-1-sources/tops20.rel