It should not be assumed that the bottle will pass the test. If it fails or if you cannot find anywhere to test it, then you have lost the use of that bottle one year earlier than if it had been sold with almost five years until test.
Testing is inconvenient because it involves two trips to a tester, will become increasingly expensive and might become more onerous in future. Many bottle owners do not bother with the hassle of tests and either stop using the bottle or sell it. Shorter lifespans when bought mean that bottles fetch less money when the initial owner tries to sell it. Initial buyers should ask for discount if the bottle is already a year old.
In any case, there is no need for shops to sell year old bottles at a new price. It does not take a year from a bottle being made until it reaches a shop in the UK. Two or three months, maybe. Therefore, buyers should ask shops to order a bottle for them so as to maximise the life of the bottle or to ask for a discount if it is an older bottle. A good shop will happily place an order or offer a discount.