Missing bottom nav bar on some html pages?

[Raymond Toy]

On most html manuals that I've looked at that have split the manual into multiple html pages, I see a navbar  (next/previous/up) at the top of each page and also at the bottom.

However, once in a while I see pages where the bottom navbar is missing.  I noticed this first at  https://cmucl.org/docs/cmu-user/html/Without-Object-Sets.html#Without-Object-Sets.  I thought this was a bug in the texinfo sources, but then I noticed that https://www.gnu.org/software/make/manual/html_node/Makefile-Conventions.html doesn't have a bottom navbar either.

Is this a bug?  An intentional design decision? (If so, I how do I know when a bottom navbar is produced or not?)

For the record, the doc at cmucl.org was generated using texinfo 6.8.  I guess the gnu make doc was using texinfo 6.7.

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Ray