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It might vary from TOC to TOC but at ours you retain your hours from the previous link and can only work within those hours unless you were spare then you are subject to whatever the agreed movement is but it goes off the spare hours in the previous link.
At some TOCs you become spare and can be allocated to any diagram as required. Very undesirable for everyone involved, crews can't plan their lives as they only know what and when they're working on the day, and obviously a massive amount of resourcing work to do to cover all the work.