Bahamian registration is C6-All of Avianca's aircraft are N-registered. Like Derg's favorite "member" said, I suspect this was a financing/insurance thing.
Side trivia: Some Aeroflot aircraft have "VP-B" & "VQ-B" (Bahamas) registrations. Rather than pay the massive import taxes for Boeing and Airbus planes, they just never import them. I guess Russia allows foreign-registered aircraft on their equivalent of an operating cert. The Russian-made aircraft have the regular "RA-" Russian registrations.
I operated a Bermudian registered aircraft several years back and we were all issued a letter from the Bermudian DGCA authorizing us to fly it with our FAA issued ATPs and type ratings. There were some nuances to flying it also, notably I remember not being allowed to do look-see approaches even though we were part 91(not that we did that kind of stuff anyway, it was just reminded to us) and the MEL was different.Did the pilots have to get Irish pilots licenses?