I too have wondered how operators crewed where they had a series one summer, then a different operator took it the next year. Doing so at some of the secondary UK points seemed difficult enough, eg Court Line operating out of Bristol for just one or two years, but Berlin must have been a considerable challenge, and yet a series of operators moved in and out of there - Dan-Air, Laker, Channel, Monarch, and others.
I suspect pilots stuck with the airline, but did local cabin crew move around between them as contracts were gained and lost ?