I'm not a specialist (euphemism

)
If I had to research them, I suppose I'd first search for their actual birth records to see if there are any marginal notes in the records (though honestly I have no idea when they introduced marginal notes at all!)
The marriage cert we saw tells us what day the children were registered, so it's just a matter of trawling through a few dozen pages each time.
To research in France, you have to know the exact place where events occurred, which doesn't make it easy. However, I see there's a very convenient search tool for marriages in the whole of the Rhône département
http://www.sglb.org/cgi-bin/gbk-searchM.plThis lists several Flinders marriages, including exact dates and places. From there, you can go back to the record search and look at the images.
When you search for records in a given place but don't know when they occurred, you can search the indexes first (tables)