The signature is the subject of the stamp
It helps to see what the slip is really about. It does not say your degree is real or your record is true. It says the official who signed underneath held that post and used that seal. The paper above is only the backdrop; the signature is the subject. Everything about getting one hangs on that single point.
Which hands the office recognises
A certified copy from a register office carries a registrar's signature, which is why civil records travel so easily. A paper from a public body carries the signature of the officer who issued it. Where a sheet has no official hand on it at all — a plain letter, say — there is nothing for the office to match, and that is the point at which people get stuck.
The practical effect is that two sheets in one envelope can behave quite differently. A registrar's copy of a marriage entry goes through without comment while a letter sitting beside it does not, even though both concern the same person and the same month. Sorting your pile by signature rather than by subject is the quickest way to see what will actually move.
Why Ethiopia adds a stamp of its own
Ethiopia has not joined the Hague Apostille Convention. Outside that agreement the older chain of stamps still stands, so document legalisation for Ethiopia means the British mark and then a consular one over it. The British stage still has to happen even though it is not the end, because it is what the consular officer expects to find already in place.
An apostille from United Kingdom to Ethiopia does not change a word of what the sheet says, and neither does the stamp that follows. Both are marks about who signed and who stamped. If the wording itself is wrong — a misspelled name, an old address, a title that no longer fits — no number of stamps will mend it, and that is worth reading through while the sheet is still in your hands.
What to settle before the envelope goes
Two things are worth settling first. One is the signature question, since it decides whether a sheet can move at all rather than merely how fast. The other is the size of the pile, because the charge lands on each document and not on the packet. Four sheets are four charges, whatever those sheets happen to say.