The Index to Registered Births was compiled using LDS films.
These films contain copies of the full Birth Registration. For anyone interested in more than one birth in the period covered rental of these films is well worth the cost, though a bit slower than getting a certificate direct.

For Registered Births post 1900 the LDS were able to film the Index Volumes.
This gives the name, year of registration, office of registration, the Volume and Page number where the Registration can be found.
Unfortunately useful stuff like parents names and actual date are not given.
I'm just starting to transcribe these index films and hope to post the result in the New Year.

I had not given it any thought, but I suppose if researchers forwarded Birth Certificate details for births post 1900 they could be added to the forthcoming index.