As you can see from Audrey’s certificate there is an ‘A’ for Occasional Copy A certificates.
Audrey was registered with both names in 1917, Koselj and Weigand and similarly in 1919, Weigand with mmn Weigand.
To clarify things slightly :
The 1917 entry for Audrey is indexed only under Wiegand. The entry is in the printed index ( with mother's maiden shown as Weigand), but not on FreeBMD. GRO has the entry ( St Marylebone vol1a p647) and has no maiden name shown for the mother which suggests that there is no father named on the entry.
The 1917 entry also has been noted as Occasional Copy A indicating a copy was submitted to GRO outside of the usual quarterly returns process. That may be connected to the 1919 entry, but may not. The "A" shouldn't appear on any certificate - it is purely an indexing note.
The 1919 entry is a re-registration to add an unmarried father to an entry - although they have married since the birth they weren't at the time, so they have both signed the entry as "joint informants", and you get the "now the wife of" wording. This predates the Legitimacy Act of 1926 so isn't the same as the more common re-registrations done after that. GRO have indexed the 1919 entry under Koslej and shown a mother's maiden name of Weigand( which technically they shouldn't).