"When were those "occasions"?"

Elected maybe but not right enough by the people. It wasn't a democracy. One example is when James VII of Scotland fled the English throne thus losing his power base from which he'd oppressed the Scottish Presbyterians the Scottish Parliament reconvened and asked both James and William&Mary to put their case as to who should be the monarch of Scotland. After the representations were considered the Parliament came out pretty overwhelmingly in favour of William and Mary and they were offered the throne! The Presbyterian majority then had James declared a traitor.