But I found a later discussion justifying the 300...

tye: Blowing out the memory consumption . . .

Ha! In response to a patch I submitted to remove the restriction (except on the initial search).

Not sure if was vroom, because the first patch is from demerphq and seems to have used a Everything engine page as a base.

The current htmlcode, newlistapproved, was implemented on Everything devel on 2000-02-10, and imported to PerlMonks on 2000-03-15. It has author credits of both vroom and nate. Maybe nate did the development and vroom imported it here. That would be a common scenario. Who knows?
Earlier versions of the code (listapproved, etc.) did not have the limit.

Perhaps interestingly, Everything2 codebase does not have "listapproved"; no htmlcode in the vicinity of 2000-02/03 seems to have anything to do with listing writeups in sections. Maybe that's not surprising; E2 doesn't have the concept of sections, nor of approval.
E2's htmlcode nodes jump from 298 to 166222, all within the month of 1999-11 (while newlistapproved is node id 4692). This implies that:

1. listapproved (and newlistapproved) were originally implemented much earlier than 2000-02; and
2. e2 deleted (or never imported) a substantial swath of code nodes which live on at pm.

Any chance of reapplying that limit-removing patch? :-}

Here's a better idea: enable the Node navigator nodelet, and then use that to "walk" the list of meditations backwards from the oldest one you've seen.