The route that actually applies
Laos has not joined the Hague Apostille Convention, so an apostille from United Kingdom to Laos is not something a receiving desk there is equipped to read. The arrangement that applies instead has two certifying stages: a British one, carried out by The Legalisation Office (Foreign, Commonwealth & Development Office), and a consular one added afterwards on behalf of Laos.
Mistakes that cost a fortnight
Most errors on this corridor are made of time. A sheet sent without an official signature comes back unmarked. A file taken to the consular stage before the British one has to go round again in the right order. A payment short by one document holds up the packet until it is made good.
None of that destroys anything. The papers survive, the fees already paid are not wasted twice over, and the only real loss is the fortnight spent discovering the problem. This is why a slow, careful first attempt beats a quick one — the calendar, not the paperwork, is what a rushed start actually spends.
The single loss that ends it
One category behaves differently. Where a paper exists in only one copy and no register holds the entry behind it, a lost envelope is the end of that document. Civil records escape this because the register keeps the entry permanently; a degree, a trade qualification or a signed personal statement often does not, and the replacement route may be slow or closed altogether.
Paying twice for a pile nobody asked for
The British stage charges £45 for each document by standard post, or £40 for each document on the next-day service open to registered businesses, so the total tracks the count of sheets exactly. A consular charge follows at the second stage, decided elsewhere and not quotable from here. Trimming the pile before anything is posted is the one saving entirely within your control.