Pilots can hold more than one type certification, but they have to keep them current. There are many pilots who fly more than one type of aircraft routinely.
Boeing tried so hard to avoid "retraining". Yet the training isn't that expensive. It's about $22,000 for an airline pilot to move from another aircraft to a 737 family aircraft. Takes about a month. And that's like an Airbus to a Boeing switch, not just between similar models. If Boeing threw in a few training credits with each aircraft (each costs about $100 million) that would have solved the problem.
Boeing tried so hard to avoid "retraining". Yet the training isn't that expensive. It's about $22,000 for an airline pilot to move from another aircraft to a 737 family aircraft. Takes about a month. And that's like an Airbus to a Boeing switch, not just between similar models. If Boeing threw in a few training credits with each aircraft (each costs about $100 million) that would have solved the problem.