Order from inside the job
When parts are ordered in a separate tab and noted on paper, the job record cannot explain why the vehicle has not moved.
Searching and recording the part against the job keeps the reason for the delay attached to the delay.
Make ETA visible
Everyone who speaks to customers needs the expected arrival. It turns an awkward call into a straightforward one.
Run a short daily review
Five minutes on the waiting-on-parts list each morning catches the orders that quietly did not happen.