Where the corridor stands today
Vietnam has joined the Hague Apostille Convention, but joining and being bound are two different moments. The treaty does not enter into force there until 11 September 2026. Until that day a British mark is not enough on its own, and a file bound for Vietnam still collects a consular mark afterwards, exactly as it did before the accession was announced.
What 11 September 2026 changes
From that date the second desk goes out of the picture. A sheet marked in Milton Keynes becomes a finished document, read in Vietnam as it stands, and the corridor turns into one of the short ones. Nothing else moves: the same office marks the paper, the same charge applies per sheet, and the same certified copy from Cardiff serves as the starting point.
That is worth saying plainly because the change is easy to over-read. It does not make older documents better, it does not shorten the British stage, and it does not reach back to a bundle already sitting on a consular desk. It removes one step from files handled after it, and nothing more.
Planning a file that straddles the changeover
The useful question is not when you post the sheet but when somebody in Vietnam has to read it. A file needed in the summer runs on the two-stage route and needs the consular days built in. A file needed later in the year runs on the shorter one. In the weeks either side of the changeover, both plans are live and the difference between them is real money and real time.
Where a deadline sits right on the line, the safer plan is the longer one. A bundle prepared for the two-stage route is still perfectly good afterwards — it simply carries a mark it no longer needed. A bundle prepared for the short route and presented too early is not good at all, and the whole errand starts again.
The Welsh end, unchanged either way
Cardiff Register Office at City Hall, Cathays Park reissues birth, marriage and death records, and the FCDO Legalisation Office in Milton Keynes marks them for the whole country by post. Neither of those arrangements is affected by the date. There is no counter in Cardiff for the marking, no appointment to book, and no change coming to that half of the route.