You can if course click on the FreeBMD site to correct errors made in the freebmd index
For instance the bride in a marriage on my tree was entered as married in Stockport but husband was entered as married in Stockton on Tees.
If a marriage place is wrong or a wrong reference was typed then when Freebmd added all the brides to the grooms they didn't match and you find perhaps 6 men and 5 women listed and the missing woman is with other people whose correct references match her incorrect one.
FreeBmd will alter errors made by transcribers in their index but as their purpose is to index the national indexes as they stand they cannot alter mistakes made back in the 1867 pages for instance.
I find quite a few errors made by the government clerks preparing the national indexes. Spelling mistakes in surnames though the name on the actual certificate is correct for instance.
Notes about these I include in a postem.
My great grandfather had the name Peter put down as his father's name on his marriage certificate but I could only find a woman with his mother's name marrying a James. His Birth certiflcate said father was James.
Dna via Ancestry has proved the name James was right. I have two new 4th cousins who are 2nd cousins removed to each other.
James' father was Hector, a subcontractor, who born in Scotland but travelled from site to site, his wife was from Worcestershire as was first child but then eight more born in England, Scotland or Wales in 7 different counties and the dna matches.
Luckily one daughter was born in Stockport and all mother's maiden names of births 1837 to date are shown for births in Stockport Reg. DIstrict bearing in mind registration boundary changes. Thus I got Hector's wife's maiden name from CheshireBMD.
Poynton (next to Stockport) registers in Macclesfield also in CheshireBMD but is a district which did not allow mother's maiden names to be shown.
The money for the dna (less than the cost of 8 certificates) has found a few blood ancestors. Worth the cash, definitely.