For my first searches on 1837online I was lucky, in that I was looking for certs. from 1913 and newer, where there is more information on the index. Flushed with success, I then started looking for earlier relatives, and found, to my horror, that info. on the index (Birth: mother's maiden name, Marrige: spouse, etc), was missing. An e-mail to 1837online about missing info. (in the description, the extra info. is present) brought a reply suggesting I look up the "Key dates for records ..." in "Resources and Guidance".
Which I did, and found the following, comprehensive information:
Key dates for records in england and wales
1 July 1837 - Introduction of General Civil Registration of Births, Marriages and Deaths in England and Wales
Births
Pre-1875 an estimated 6 to 10% of births NOT registered <=== !!!!
1875 more rigorous enforcement of compulsory registration <=== !!!
September quarter 1837 to June quarter 1911 -- only first two full forenames, subsequent initials, registration district and reference number
September quarter 1911 to present -- only first forename, subsequent initials, registration district and number but also includes motherīs maiden surname.
Marriages
September quarter 1837 to December quarter 1911 -- only first two full forenames, subsequent initials, registration district and ref number
March quarter 1912 to September quarter 1962 -- if female was previously married, index shows maiden name and married name
March quarter 1912 to present day -- surname of spouse added
Deaths
1875 enforcement of compulsory registration
September quarter 1837 to June quarter 1911 -- only first two full forenames, subsequent initials, registration district and reference number
September quarter 1911 onwards - only first forename, subsequent initials, registration district and number
September quarter 1837 to December quarter 1865 -- no age given
March quarter 1866 to March quarter 1969 -- age at death given
June quarter 1969 to present -- exact date of birth given
1911/12 are the the important dates, as more info. came in the index itself, making life much easier for us !