A new problem to watch out for.
I have two people with birth registered in 1896, index numbers written down years ago.
I visit the index to see what district this was in, search the index for 1896, they are not there !
These two were born in November 1895, it turns out.
This business of using the exact actual event date, but keeping it hidden and showing the index reference number of a different year, has a downside as well as an upside.
And the silly business of making users try smaller and smaller subdivisions of the year to pinpoint the actual event date, what is the point of that exactly ? You end up accessing their database server 20 times, instead of once. They might as well just display it.