>>5000 labels is easy to reach if you are using the label mechanism
>>extensively.
>
> This is real life with critical editions in the "classical" style
> where footnotes don't refer by footnote marks but by line numbers.
> ednotes.sty originally used three labels for one footnote
> and broke with, say, 400 pages.

A LaTeX translation of the largest of the four religious texts
(English language) in Jon Bosak's 1998 XML demos might reasonably have
at least 24000 labels.
See  http://www.ibiblio.org/bosak/
     http://metalab.unc.edu/bosak/xml/eg/rel200.zip


                                    -- Bill