Two stages, not one
Gabon has not joined the Hague Apostille Convention, so one British mark is not the answer for a paper used there. Documents bound for that country need embassy or consular legalisation instead, which puts a second desk behind the first. No apostille issued in Bristol for use in Gabon carries weight by itself, and nobody at the consular end reads it as a finished article.
Where the file stops
The FCDO Legalisation Office at PO Box 6255, Milton Keynes MK10 1XX works by post and sends the paper back to whoever posted it. That return is not a quirk of the design; it is simply how the office runs. The practical result is that an apostille from United Kingdom to Gabon reaches your table again, whole, before anything further is done to it.
Almost nobody uses that moment. The envelope is opened, the contents are glanced at, and the lot is re-posted within the hour. Yet this is the last point at which a wrong sheet costs one reprint rather than a whole run, because every stage after it belongs to somebody else's schedule and somebody else's charge.
Three things worth a slow look
Whether the sheet is the one the reader abroad actually wants. Whether the names and dates on it match how you write them elsewhere. Whether the British certificate is still fastened to the paper it describes. None of the three is examined by anyone later on the route, because no desk after this one has ever seen your papers before.
What the pause costs
Nothing, in money. In time it is the difference between posting on a Tuesday and posting on a Thursday, set against a consular stage that keeps its own hours anyway. Bristol Register Office at The Old Council House, Corn Street, Bristol BS1 1JG can reprint a civil record if the pause turns something up, and a reprint now is far cheaper than later.