Read what is already there
Papers pick up marks over a lifetime. There is the seal of the office that issued the sheet, sometimes an endorsement added by a solicitor for a job long finished, and now and then a certificate from a run to another country that never got used. People look at all this and assume they are most of the way there.
They usually are not, because a route asks for one particular mark from one particular office. Nothing else substitutes for it, however official the other marks look. Sorting the sheet out means naming each stamp and the desk that applied it, which takes a few minutes and saves a wasted posting.
The mark Laos is waiting for
An apostille for Laos is not the one that closes the file. Laos has not joined the Hague Apostille Convention, so document legalisation for Laos runs through a consular desk after the British stage. That desk applies its own stamp and is not moved by what else the sheet already carries.
There is no apostille issued in Manchester for use in Laos to be had over a counter, and an apostille from United Kingdom to Laos on its own leaves the chain unfinished. Anyone weighing up what you need for an apostille for Laos is really asking which desks are still ahead of them, and old seals do not shorten that list.
When a clean sheet is the cheaper move
Manchester Register Office issues certified copies of the civil records registered in the city, from Heron House, 47 Lloyd Street, Manchester M2 5LE. Ordering a fresh one costs a fee and a wait, but it removes every argument about a marked-up sheet at a stroke and keeps the certificate you rely on out of the post entirely.
It is worth doing when the paper is crowded, worn or hard to read, and worth skipping when the sheet is plain and the only mark on it is the issuing office's own seal. The choice is yours to make before anything is sent, and it is much harder to revisit afterwards.
What carries forward and what does not
A British certificate already on a sheet was applied by the office that handles this stage, so it is not something to buy again. Marks made abroad belong to the chain they were made in. Keep that distinction in mind and you will neither pay twice nor set out expecting a foreign stamp to do work it cannot do.