What you probably need to factor in is that there is no complete turnover every year. Some people might spend multiple seasons there, or at the very least retur

What you probably need to factor in is that there is no complete turnover every year. Some people might spend multiple seasons there, or at the very least return on a regular basis for research. Then there is also support staff who might work there for multiple seasons. So there likely is enough overlap between people that have been there for longer and new people to pick up on the accent. The latter is something that people subconsciously do fairly easily.