Sort your papers by what can be replaced
The route to Georgia is identical for every document, but the cost of a lost envelope is not. Some papers a public office can reissue on request; others exist only as the sheet in your hand. That single difference is the real risk in this errand, and it is settled by which sheet you choose to put in the post.
Why a fresh copy is the sheet to use
Sunderland Registration Service issues certified copies of births, marriages and deaths recorded in the city, and each one is a fresh official document rather than a duplicate of yours. An apostille issued in Sunderland for use in Georgia sits on that copy perfectly well, because the certificate is added against the registrar's signature, and the registrar signed the copy too.
Georgia's side, and the single stamping step
Georgia joined the Hague Apostille Convention in 2007, so a British paper going there needs one certificate and nothing after it. The FCDO Legalisation Office adds it and returns the file by post. Searches for document legalisation for Georgia describe that same single step, which is why the planning here is really about the paper you send rather than the process it goes through.