If you have cared for someone with dementia, this isn't so surprising.

It isn't a monotonic decline with memories disappearing forever. It is like wave upon wave of changing capacity at different time scales. The general trend is deterioration, but there are frequent periods that can almost seem like remission.

There is a well known daily cycle referred to as "sundowning", where the sufferer tends to come unraveled later in the day. The next morning, they'll be more functional.

Later in the progression, you can see much higher frequency variations. Like periods of disorientation and confusion interspersed with periods of lucidity all within a single sitting or conversation.

In those periods of greater lucidity, recall of the past can be more accurate. General listening comprehension, speaking, and logical thought also seem more normal.

Edit to add: I sometimes wonder if the belief in terminal lucidity is one of those logical fallacies which support lots of superstitions. Are we just fixating on the final wave in this chaotic wave train, and forgetting all the other waves that happened before it? Or is it that more caretakers are engaged and observing these waves towards the end, e.g. because the patient is known to be in the terminal phase..?

Same thing happens for other disease. Some kind of last honey moon period where your health improves and often followed by a catastrophic relapse.

I'm nobody but it makes me feels there's an economic system issue, the body gradually degrades but has the ability one last time to inject a final wave of change to try restore a proper state but the resources are too short and so the attempt cannot sustain itself.

I wonder if research is happening on this aspect.

i’m skeptical how much of a real thing this is vs particularly type of appealing story to the human psyche