The route, stated plainly
An apostille for Democratic Republic of the Congo is not accepted. That country sits outside the Hague Apostille Convention, so a British paper going there requires embassy legalisation instead of the single-stamp route. Knowing this on day one changes what you buy and in what order. It does not change the groundwork, which is the same for any route: the papers in the bundle have to describe one person, consistently.
One person, several spellings
Most files that stall are not stopped by a missing stamp. They are stopped because the name on the degree is not quite the name on the passport, or a middle name appears on one paper and vanishes on the next. Readers searching for what you need for an apostille for Democratic Republic of the Congo rarely expect this to be the answer, but a clerk who cannot match two papers has no way to proceed and no reason to guess.
Fixing a spelling at its source
A certificate cannot be corrected by the office that stamps it, only by the office that wrote it. For civil records that office is the register office. Newcastle Register Office can issue a fresh certified copy of a birth, marriage or death entry it holds, and a clean current copy is far better company for a legalisation chain than a worn sheet from decades ago. Order the copy first, then move.
What the British side would have done
The Legalisation Office (Foreign, Commonwealth & Development Office) issues every British apostille, working by post rather than over a counter. An apostille issued in Newcastle upon Tyne for use in Democratic Republic of the Congo would come from that same office, at £45 for each paper by post or £40 for each paper on the next-day service open to registered businesses. It simply is not the certificate this destination reads, so an apostille from United Kingdom to Democratic Republic of the Congo is a purchase with no landing place.
Carrying the thread through the chain
Document legalisation for Democratic Republic of the Congo passes your file across more than one desk, and every desk reads the names again. A mismatch that one clerk waved through will stop the next one, so a file can travel a long way before it fails. Sort the spellings before anything is stamped, because a correction made halfway along means the stamped papers behind it are now describing the wrong person.