Update: Well, the very next business day after I post this guide and guess what - deliveries sent by sellers over a 3 week period all turned up AT ONCE. As that wonderful saying the Yanks say, "Go figure".
------- Original text follows:
I suspect there are dodgy dealings going on at the Royal Mail sorting office in Neasden, London. There are 3 weeks of deliveries, none of which I've received. For around 200 items over a 3-year period, about 5 (thankfully small and cheap) items have gone missing, but once before there was a roughly 2-week period where nothing arrived and they claimed they had never made it. This was even when sellers had proof of posting. Such issues were never resolved and I ended up either getting a refund or just writing off the loss. Now, I am worried this is happening again. Various items from various sellers all seem to have gone into a black hole. Therefore it may be worth making sure proof of postage is always requested over the Post Office counter, and I may request that you send me a copy by e-Mail with the tracking number clearly visible so I can challenge the Neasden sorting office. I strongly suspect these occurrences are caused by agency cover staff stealing packages.