The ordering system for Teams goes something like this.
IC of the fire, and his/her bosses discuss the need for a team well before it is ordered, for new, building fires. For established fires, many people know the Team schedules and likely rotation times. Again, ordering replacement Teams is discussed well before the actual order. Longterm fires with increasing complexities also plan the need for more Team orders, as well as zoning or splitting fires. This is not something done spur of the moment.
People know what Teams are up. It’s not a secret. Some can look in the ordering system and see the orders being placed ( but not yet assigned). The IC is usually alerted a Team order is being discussed, and in the larger situations, the alerts, which the IC passes down the Team, can occur days ahead of the actual order. In situations where Team rest days and days off are a critical concern, a resource, including a Team can be told " when you come back from R&R, you will be assigned to this fire".
Lastly, the not always reliable, rumor mill.