Read the names before anything moves
Put the papers on a table and read the names aloud. It feels slow and it takes ten minutes. What you are hunting for is small: an initial on one sheet and a full middle name on another, a hyphen that appears only once, a surname that lost an accent somewhere along the way. Each of those is a question waiting for someone you will never meet.
Doing this before you spend anything pays here in particular, because an apostille for Papua New Guinea is not accepted as the finish and the file passes through more hands than a short route uses. The earlier a difference surfaces, the fewer of those hands have to look at it twice.
Papers made at different times say different things
A record is a snapshot of the day it was made. A birth entry holds the name registered then; a paper drawn up later holds the name in use later. Marriage and a formal change of name both leave that pattern behind, and none of it means anything has gone wrong. It only means your bundle tells a story that somebody has to follow.
The way to help them follow it is to send papers that connect. If the reason for a difference sits in a document you already hold, it belongs in the bundle with the rest. If it does not, the gap is still far better named by you at the start than found by a desk at the end of a long route.
Papua New Guinea's position, and what it adds
Papua New Guinea has not joined the Hague Apostille Convention. So document legalisation for Papua New Guinea runs through consular channels, and no such item as an apostille issued in Birmingham for use in Papua New Guinea exists to be bought. The British stage still has real work to do; it simply is not the last of it.
That is why an apostille from United Kingdom to Papua New Guinea is the wrong thing to build a plan around, and why a name problem is dearer here than elsewhere. Every extra desk is another reading of the same page, another envelope, and another chance for a difference to be spotted by somebody who can stop the file.
Where a matching copy comes from
For births, marriages and deaths the answer sits close to home. Birmingham Register Office at Holliday Street, Birmingham B1 1TJ issues certified copies of the entry it holds, so you can order a fresh one showing the registered name and keep the record in your own drawer out of the journey altogether.
Order every copy you need in one go. The British charge is £45 / document (standard postal); £40 / document next-day (registered businesses), and it attaches to each document rather than to the envelope they share. Copies ordered together also read identically, which is the whole point of the exercise.