how do you treat, or how do you label busduct plugs? Do you label at all or what is your customary practice in labeling busduct. For example, if the busduct is lower to the ground, say 12 feet above the floor, do you label each device?

The incident energy of each plug should be based on the busduct itself, not what is inside of the plug. Labeling individual plugs is a waste of labels and may contribute to safety information overload. We labeled every 2 or 3 10 foot busway lengths.
This is similar to not labeling each individual fusible switch or breaker in a switchboard or panelboard.