Count the desks before you count the stamps
The first number on this route is not a fee. It is how many places will want to hold your record. Each of them keeps what it is given for as long as it needs, and some keep it for good, so a single sealed copy passed from hand to hand is a queue you have built for yourself.
Manchester Register Office at Heron House, 47 Lloyd Street, Manchester M2 5LE will print as many certified copies of a civil record as you order. Doing that in one request is much faster than coming back for a second. Your own original stays with you throughout, which is the point of ordering copies at all.
Afghanistan's position on the Convention
An apostille for Afghanistan is not the closing certificate. Afghanistan has not joined the Hague Apostille Convention, so document legalisation for Afghanistan goes the consular way, with a further desk after the British one. That extra stage is what makes the copy count matter, because every added desk is more time a paper spends away from you.
There is no apostille issued in Manchester for use in Afghanistan sitting ready at a local office, and an apostille from United Kingdom to Afghanistan would not be read as final at the far end in any case. Anyone asking what you need for an apostille for Afghanistan is really asking about the consular chain, and the honest first answer is: enough sealed copies to feed it.
Every copy travels on its own
Each certified copy is a separate item all the way along. The Legalisation Office charges its fee for each one it stamps, and a consular desk treats each as its own file too. Nothing is bundled and nothing is discounted, so two copies simply cost twice, which is worth knowing before the order rather than after it.
The upside is that the copies are independent. If one is held by an office overseas, the other is still yours to use, and a delay to one does not stop the other. Splitting the risk that way is why people who have been through this route once tend to order a spare the second time.
What the copy count does to your timetable
Copies ordered together move together, so the extra ones cost almost no extra time. Copies ordered a month apart run two separate races through the same offices, and the second one starts from cold. Post times and desk workloads vary, so no fixed date can be promised for either, which is another reason to send the whole set at once.