A computing device obtains a machine-readable code encoding a group identifier, and decodes the group identifier to identify each unit identifier of each of a plurality of tracking units. Decoding includes identifying a first portion of the group identifier that identifies a first unit identifier of a first unit, and identifying a second portion of the group identifier comprising a multiplier identifying a number of the plurality of tracking units that are within the grouping. The computing device sends a request to a management service for a first user to obtain custody of the plurality of tracking units. The management service reassigns custody of the plurality of tracking units from a second user to the first user, without obtaining input from the second user. Another computing device associated with the second user updates a displayed status to indicate that the first user now has custody of the particular tracking unit.