The route Guinea-Bissau works with
Guinea-Bissau has not joined the Hague Apostille Convention. Papers travelling there require embassy legalisation instead of the single-stamp route, and an apostille for Guinea-Bissau is therefore not the certificate its offices are set up to read. That is the starting point. The more useful idea behind it is one that survives any change of country: the paperwork exists to serve a decision that a human being makes.
Recognition is something a person does
It is tempting to think of a legalised paper as carrying acceptance around inside it, like a charge in a battery. It does not. Somewhere at the end of the journey a clerk picks up your file, looks for the marks their own rules tell them to look for, and forms a view. Every stamp in the chain is an input to that moment. None of them is the moment itself, and none of them can be spent in advance.
What each mark is actually for
A mark added by a British office closes a gap in knowledge. Nobody in Guinea-Bissau can be expected to know a Newcastle registrar's handwriting, so a body the reader already deals with vouches for the one before it. Read that way, document legalisation for Guinea-Bissau is a translation of trust rather than a fee for a certificate. It builds a short line of familiar names between your paper and a stranger.
Where the British side stops caring
The Legalisation Office (Foreign, Commonwealth & Development Office) issues all British apostilles by post, at £45 for each document or £40 for each document on the next-day service open to registered businesses. An apostille issued in Newcastle upon Tyne for use in Guinea-Bissau would be an entirely genuine British act. What it would not be is an act the receiving side has agreed in advance to rely on, which is the only thing that matters here, so an apostille from United Kingdom to Guinea-Bissau leaves the real decision untouched.
Making the decision an easy one
Since a person decides, aim your effort at that person. Order a fresh certified copy from Newcastle Register Office so the sheet is clean and legible. Read the names across the bundle and make them agree. Readers looking up what you need for an apostille for Guinea-Bissau usually want a list, and this is the honest one: right route, right copy, matching names, nothing loose, nothing missing.