They run out on different weeks
Mailers, padded envelopes, kraft and void fill often run out on different weeks. Packaging Suppliers can still take them as one order. In by 3pm, they leave together.
The £50 ex VAT free-delivery line is the combined goods total. Separate checkouts can each fall under it.
Do not mix up the jobs
A grey mailer is the outer for soft goods. Kraft wraps. Gummed tape seals. Void fill packs out a carton. Grip seal bags, food approved and at least 30% recycled, are usually an inner bag from GL0 to GL15, not a posted outer.
Clear food bags in 100 gauge or 200 gauge are a different film again. They are not mailing bags.