Regarding Bournemouth, Tony Merton Jones' book provides (as ever) more information. After Channel went under in February 72, BMA temporarily picked up Southend, Stansted and Bournemouth to Jersey. The first operation out of Bournemouth was Friday March 3 with Viscount APNE. This lasted for just 4 months until the permanent licences came into force, when BMA kept Southend and Stansted, but Dan-Air took over Bournemouth from July 1 with 748s.
Although APNE was coming towards the end of its time with BMA (it went off to Israel at the end of the summer) this was indeed the time the seven SAA Viscounts were coming on line so BMA would have had spare capacity. Evidently though they were not enough as BMA bought another seven prop aircraft the next year, four Viscounts from Lufthansa and three Heralds from South America.