but to have 3 items in one month never arrive seems to be accessively high in lost shipments through the mail.
It does seem high.
I'd be talking to your postmaster (not at the postal Outlet, the post Office) about any suggestions they may have.
Since you were refunded, should we assume that all of these were Tracked but none showed Delivery?
Or were they untracked- where the seller gives up Proof of Delivery in favour of lower shipping costs?