Hello,
in the manual
https://orgmode.org/manual/Footnotes.html#Footnotes
it says that footnotes[fn:1]
[fn:1] look like this
but actually[1]
[1] works as well and looks even better.
So why this option is not documented?
I would think that's so because canonically Org mode using [fn:1] style. It looks like you are manually typing the footnote refs and definitions.
Try using C-c C-x f binding.. you will see that Org inserts the footnotes in the documented style.
I would say that the "fn"-style footnotes remove any kind of ambiguity..