WYSIWYG: you're right, "They can't be split", they're here, as they are.
The point being made is that (in future) they should be split before they get to much over 40 items. An automated system would ensure that cross references were available. I have split a couple, and cross referenced, and then gone back to the original to remind people that the continuation is elsewhere (others with a greater input than I do so frequently!). But (human nature being what it is) people continue to post to the original thread (and often to the new one as well).
An 'automatic' split might (I don't know enough to be sure) ensure that no new posts could be posted to the first section, and re-direct them to the second (3rd,4th) section.

CHEERS

Nigel