ED-K-Class Lethe Scenario: Without prior warning, all knowledge of a well-known concept or item is forgotten, and the thing is now alien to the observer.

A big Lethe Event already happened. The world used to be more comprehensible to humans; we could see all of the electromagnetic spectrum, we understood quantum physics, etc. but the concepts were erased from our mind by the effects of SCP-3911. We're already living in the post-apocalypse, we just don't have the information available to process that it happened. Lethe Events still occur in this post-apocalyptic seemingly-normal world of ours because effects lingered after the big event.

Narrative order:

Handbook SCP is an example of something forgotten from human memory. We can tie Rimple's concept of humans not actually having flesh anymore into the body horror of this SCP.

Dog Tale is a glimpse into what Lethe Events do to the human psyche, and the mechanics of how forgetting works.

3911 is the by-the-book scientific documentation of the anomaly of Lethe Events.

GoI doc and Rimple's tale will be the finale, revealing the plot twist that we've already experienced a Lethe Event.