What goes wrong
Count the soft dispatches of that size.
Packaging Suppliers lists Mailing bags for this line. The mailroom runs out of one size first. That size is the reorder, not a mixed assortment.
The check before you reorder
Reorder grey, and the size.
Keep each size in its own shelf slot.
Dispatch on that order
A Friday order on Packaging Suppliers that includes Mailing bags aims for Monday. A bank holiday on Friday or Monday moves that delivery. The 3pm cutoff is still the same-day dispatch rule.