CH 1983 Stamp Day Bellinzona TI, society covers 2 flights cancelled 3.12.83 Bellinzona and Locarno with add-on cancellation

Switzerland 1983 Stamp Day Bellinzona TI,
society covers "75 anno Fondazione Circolo Filatelico di Bellinzona"
two registered mails transported with special flights on the occasion of Stamp Day in Bellinzona:
1. flight "VOLO BELLINZONA-MAGADINO" gestempelt "3.12.83 6500 Bellinzona", rückseitig Ankunftsstempel "3.12.83 6600 Locarno",
with black add-on cancellation "BELLINZONA - Giornata del Francobollo - 2.-4.12.1983 - ESPOSIZIONE FILATELICA",
2. fligth "VOLO MAGADINO-BELLINZONA" gestempelt "3.12.83 6600 Locarno", rückseitig Ankunftsstempel "3.12.83 6500 Bellinzona",    
with green add-on cancellation "BELLINZONA - Giornata del Francobollo - 2.-4.12.1983 - ESPOSIZIONE FILATELICA",
luxury conservation, rarly offered.