During his lifetime, mainly. I just remember a time when the women's soccer team was looking for a nickname - all the iconic animals had already been spoken for - and came up with The Matildas. And there was a bit of chit-chat about what a matilda might be and no-one really knew.
Bilby, do you mean scant evidence of its usage today, or scant evidence of its ever having been used outside the poem/song?
I would argue it's kind of like mome raths or brillig--sure it wasn't (and isn't) used much outside the poem, but by virtue of the poem achieving great visibility, the terms have now entered the language, so... Paterson's job here is done. :)