Genie, thanks for the appreciation. I didn't really mean to argue against the notion of expiry dates (however described), but to inject some experiences and how a bit of knowledge of relevant biology and culinary traditions can be applied. What I do at home for purely domestic and personal purposes isn't subject to much in the way of statute law but if I do for outsiders or in the workplace the whole panoply of the law applies, even outside the (reputedly litigious) USA.
And I do have a relevant comment about tea tree oils. Whatever it says on the outside of the packaging, there may be no intrinsic difference between tea tree oil and melaleuca oil, because "Tea tree" is the common name (in English) for all the species of the genus Leptospermum and many species of the genus Melaleuca. And there's quite a few species in both genera. The species that has been marketed (dare I say "hyped") is Melaleuca scoparia, commonly called "Manuka" in English, from its common name in NZ, but it also occurs in Oz. [There was a thread not long ago on the pronunciation of manuka and the properties of various honeys and tea tree oils.] There are oils on the market that have been made from other melaleucas (M. squarrosa is one example) and from various Leptospermum species. There have even been some oils from Eucalyptus species marketed as having antibiotic/antiseptic properties. All three genera are members of the family Myrtaceae so it's no surprise that essential oils from various such species should share such properties.
Before the Botany Library foyer at Melbourne Uni was refurbished in the early 60s there was a row of about 30 "sealed" glass cylinders ~4" in diameter and ~18" high; each was named with a species of some member of the Myrtaceae and was almost full of oil from that species. It was the result of some project on economic botany that had been done in the 1930s and the collection had been displayed there ever since. Every one of them had oxidised to some extent and nobody was prepared to guarantee their biological properties. They all got discarded while my back was turned; I suspect someone wanted to take the glass (attractive in its way) for a personal collection.
And I offer a small take on the antiseptic properties of Melaleuca Oil. SOme years ago I was doing some research into the ethnobotany of the Bloomfield River area (just north of the Daintree World Heritage Area in north Queensland. I'd made the mistake of taking shelter in a camp that had not been used for some months and every flea egg in creation had hatched; they all wanted a piece of me and the skin became infected. All the locals said "Put tea tree oil on it!" The bottle had a label "Melaleuca Oil" and I had my doubts about the efficacy of this approach. Ever the rational scientist I put the oil on one side of my body and left the other free of it as a control. The treated side (with the oil) got worse while the untreated side remained the same as it had been. I went off to the District Nurse at Wujal Wujal (once called the Bloomfield Mission) and she gave me some oral antibiotic which cleared both sides up in two days.