Okay, it seems that explanation of how it works is not remotely correct. I'll replace it with a correct one.
Any suggestions afterwards to
change it could be heard, but should be a new topic.
EDIT: Copy-paste of the new explanation from that topic:
In terms of how the game actually selects which one to display, it will pick the last one in the file that fits the following conditions:
1. The player has saved enough lemmings to fulfill the condition.
2. For the specific level in question, the save requirement of any earlier-in-the-file postview text that fulfills condition 1, is lower than (not equal to) the save requirement of this text.
There is a special case - if a text's condition (not just "what it calculates to in practice") is either "save the requirement exactly" or "save 100%", it does not need to pass condition #2 (it still must pass condition #1 of course).
I also discovered another somewhat related bug while investigating this: When calculating which postview message to display, the level's lemming count is calculated as if all Cloner pickup skills in the level only provide 1 skill, even if they actually provide multiple. This is fixed in commit 37fe2be, and will also be backported to a V12.10.2 release if one occurs.