In 1837 C of E ministers automatically became empowered to conduct registrations of marriages, and return the details to the local registrar. C of E churches had two registers, one of which belongs to the local registrar and is sent there when full. The other is now deposited under C of E rules at a record office designated by the diocese, which is the copy we can access.
As far as I understand, the registrar had a separate register for each Non-Con church, which was taken there and brought back every time the "Registrar Attended". There would also be a register used for Registry Office marriages. The rules changed somewhere around 1900, to allow Non-Cons to register their own marriages if they wished, so after that they had two registers.
The marriage locator works on the principal that the local returns to the GRO were assembled in a regular order, C of E first, in alphabetical order of church, followed by Non-Con & RC in a set order, then Registry Office. Therefore within one district, the page numbers at the GRO for each quarter were similar for each church, but not identical. The first part can be "solved" from registers in record offices, but the pattern of the higher page numbers depends upon extracting information from registers we are not allowed to see.
You could say we have a lack of Freedom of Information due to religious discrimination which occurred between 1837-1900!
