You can see if there is already a candidate proposed for a specific vacancy via the ‘P’ icon on the right side of the Crew Change Screen.
To see the details of the proposed candidate, select the respective crew change line, press Details and then select the Candidates Proposed tab.
So, for the below example, the deadline to propose a suitable 2eng candidate would be a few weeks before the 21st of July, and as you can see, the Russian agency Sunrise Marine has already proposed a candidate and the status is Pending.