To clarify ....Occasional Copy does mean that a copy of the register entry was submitted to GRO outside of the usual quarterly returns process. This almost always will be due to some sort of correction, or change, to the register entry.
In such cases there is no "original copy" to order, because the register entry itself has been changed, and any certificate issued will always reflect that change ( but it should be clear what the change has been). Just order as normal.
This is quite different to a re-registration where there will be more than one entry relating to the same birth, sometimes months or years apart ( which therefore have completely different references), and for which you can order certificates from either entry and they will be different.
Thanks for the link. I read it. It may apply to my case. I am looking at a birth registration for a person (say Ann Smith) who has different details on the GRO and on FreeBMD. The birth year is 1929. On the GRO her MMN is given as - (a hyphen). On FreeBMD her MMN is given as Smith (ie. the same as the child).
It is quite normal to find different results when searching on the old paper indexes, as used on FreeBMD, and the newer GRO on-line index, because they use different indexing rules.
Where there was no maiden shown on a birth entry, the old paper indexes, from 1911, just repeated the mother's surname in the maiden name column. In the same circumstances, the new GRO index (correctly) leaves the maiden name field blank.