Maybe the doc-string of `gnus-summary-limit-to-age' could mention
negative numbers too?

Part 2: <menu-bar> <Gnus> <Limit to> <Articles>

And the menu text "Gnus/Limit to/Articles" (`/ n') might be changed.
At least for me, the current label is inexpressively (of course
limiting deals with articles, but with _which_ articles?).

,----[ C-h f gnus-summary-limit-to-articles RET ]
| gnus-summary-limit-to-articles is an interactive compiled Lisp
| function in `gnus-sum'. 
| (gnus-summary-limit-to-articles N)
| 
| Limit the summary buffer to the next N articles.
| If not given a prefix, use the process marked articles instead.
`----