It would be helpful to have a line on all label formats for shipper use. This would allow local delivery instructions such as "use back door", "gate code 1234", "leave with security" etc. Or a customer phone number for international when you already used every line and shortened as much as possible to fit.
This line can either self populate from a notes section on order forms with WooCommerce (for example), Volusions etc. Or be filled in at time of label creation.