I was more wondering if you only had perhaps the one example of Eliza and Charles with these extra names, and whether it may have been added in error (on the death certificate for example)?
Something that just occurred to me since you say that Charles added the name of his second son ….
Do the additions of these names tally with the deaths of their own parents? To me it might make more sense to add the name of a deceased parent rather than a living child. It is possible that the child could have been named after their grandparent anyway.
Just throwing round a couple of ideas, but don’t have any real explanation.
Added: I was not aware that there were any useful surviving censuses for Australia apart from the odd name here and there.
Apologies for the late reply. I got delayed wiring downlights in our roof. Not as fast as I once was
Eliza's mother was also named Eliza, but the old sister was Emily. Which is the only other in the family with that name.
Sisters Eliza and Emily Thorne both immigrated to Australia from Hampshire after their parents died. So these are the Census I'm referring to.
This line and names become even more interesting in the following generation in Australia.
Eliza and Charles's first son moves to a cattle station in NSW and he changes his last name Koster to Nelson. On speaking with the direct descendants of this particular family, they said it was during WWI which is the only reason they could come up with for the name change.
And now more recently I began digging into information on one of the younger Koster daughters. Since initially there was almost no information on her apart from a birth in South Australia and a death year in Melbourne. Turns out she to changed her full name, not once, but twice in 3 years. I got lucky with the info, as there was quite a large inquest with plenty of documentation on the death (once I found it under the new name). It was big news for the time, appearing in a little over 50 newspapers throughout Australia in 1921.
This family line is certainly interesting, to say the least.