Parcels might be delivered separately, but they are sorted together.
For metro areas anyway, this is how redirections are “actioned” (and in some cases why they aren’t): the mail is sorted into the slot the corresponds to the address on the envelope (large parcel that don’t fit in the sorting frame get set aside). When the postie has finished sorting the mail (often it’s the same person who delivers it), they then go through a book of redirect stickers and pick out all the mail that is to be redirected.
There might be a dozen or more addresses with a redirect on them on any given day. If a parcel doesn’t get redirected it would be because it’s in a different pile (this would be where the process is failing, I suspect). Parcels probably don’t get the same attention as letters - most parcels are individual orders, not subscriptions, which would mean the address is likely to be correct. (A letter from your super fund, on the other hand…)
If the postie is delivering the parcel they might catch the fact that the addressee’s name is on their redirect list, and take it back at the end of their round. If the parcel goes to the contractor, they have no way of knowing and just assume that the parcel is supposed to go where it says on the front.
