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Used to indicate someone has been contacted to attend an event, but not yet responded or confirmed they are able to attend. Generally used in conjunction with notes which are entered indicating the latest contact someone had with the person.
Tentative
Used to roster someone to the event, but are still awaiting confirmation from the person that they are able to attend. The person rostered can confirm themselves via the home page and also when viewing the event details.
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By default, people that are newly added to the roster are given the status 'Confirmed'. You can change the status that people are initially given by going to the 'Options' dropdown menu on the right-hand side of the screen, just above the list of currently rostered people.