Chimonger, your point #5 reminds me of the final scene in Verdi's "La Traviata" wherein the dying Violetta suddenly feels stronger, declares that the pain has left and expresses hope that she might live after all, then falls back onto the couch and dies. This phenomenon that you write of has probably been observed throughout history.

I did read recently some research that indicates that dementia patients can react to recent events that they do not apparently "remember"--but there is something back there that does retain it. My brother had Parkinsons, and showed memory problems before the physical symptoms. But even late in the disease, he would occasionally "come back" for a short period--so there was more there than he could usually communicate.

"They"...do research; sometimes with too few people to get respectable trustworthy data, but enough to see a possible trend or a clue. That can seem so important, it gets reported, or not;. The prefacing summary may be written correctly to reflect the contents of the study, or, incorrectly to reflect the bias of the author of the summary [notable scientific figures will often be asked to write a credible summary, as this gives more social/scientific weight to the study crew and the study; it's known that fewer professionals actually read the substance of a study, only read the summary to save time--trusting that is written honestly/correctly].
Based on no known study but observation during patient care, and understanding that the mind is non-local; that the brain is the interface to the mind, and that the progress of Alzheimer's changes over time [so does dementia]....that means the memories are still stored, just the pathways to access or process them change.
The disease process is Not static; plaques increase, decrease or shift over time, depending on conditions. A Doc telling someone those plaques, deposits or other tissue issues don't change, is very similar, in my mind, to those of a Doc who pronounces a fixed, known time limit [expiration date] for a patient, as if they had an expiration date stamped on the bottom of their foot!
Observed:
1. Grandma showed signs of mental difficulties at least 5 yrs. or more before it got bad enough to get diagnosed. Later into her Alzheimer's, she couldn't remember her own daughter [who lived at great distance and rarely saw her or spoke with her...and had colored her dark brown hair blond]....But she remembered one granddaughter she rarely saw [who still closely resembled the child she'd taken care of many years before]. The grand daughter could easily follow along and converse with G'ma, because she knew her history, even as G'ma spoke of it in bits and pieces. This surprised the nurses, who had told the granddaughter that G'ma couldn't speak anything coherent.
2. Patients have often been really "out of it" with dementia, Alzheimer's, or even things like post-stroke or other illnesses, yet pulled things together enough, periodically or right at the end, to suddenly resume recognizing ideas, memories and people "forgotten" due to the illness.
3. As someone who's had a stroke event, immediately after which this mind seemed off-line entirely, the brain somehow quickly or slowly, started reconnecting the links between memory pathways.
Some things took time and rehab to reconnect, but some things came back without too much work. . Inside my head, it felt like there were thoughts and connections out there, that the brain had yet to reconnect to find yet...I felt those were there, just inaccessible for a time...that if I stumbled around in there enough, or worked at it, they'd come back. Most of them have, but it's taken almost 20 years; AND that's related largely to what I choose to consume or be exposed to.
4. Patients have shown evidence they remember things in all or part, if they are interrupted from their immediate role as a sick person. This might happen when someone is more heavily using their role or position as a sick person [they may feel need to escape something they can't tolerate, and this is their only perceived method of escaping, or, they feel the need of attention, and being sick is their only way to be ok with getting attention [socially acceptable]...They are still actually very sick, however, the current sickness exists, in all or part, because the person felt the need of it, by their habits and behaviors...need of being sick, is a tool, dysfunctional as it might be, to get what one needs. THIS is largely socially unacceptable to even speak of, much less believe it happens, because for most, that concept is seen as 'blaming the victim', and well, we are not allowed to do that....framing that concept as 'blaming the victim', is INCORRECT. This concept is about spiritually, socially, etc. taking responsibility for our choices and the potential outcomes of those choices. It may, or not, work as an explanation for all ills...unless and until we are able and willing to view illnesses and accidents in the context of someone's whole life and their experiences and choices over a lifetime. . Science has no clear or good way to do that kind of assessment, yet...most professionals, and even more public, still are unwilling to give psychological/ emotional issues their proper valid place in the scheme of things; nutrition is pretty much, for all the current marketing, not even yet considered as a way to remedy or heal ills, even though history and science support it. And we have an even longer road to travel, to reconnect our inner spiritual awareness[not religion] with our outer world, or our physical bodies.
5. Dying patients who have been being comatose, or near to it, who have lost ability to communicate, will often "rally" shortly before they die, for minutes, an hour or a few days, even. These will suddenly have refreshed abilities, talking, communicating clearly, even get up out of bed and do things not done in months or even years. Once they do that, and maybe have closure with family who now has their hopes up the patient is getting well, they then let go of their body, dying. What are the commonalities in Those cases, and why has that not been heavily studied??
Lessons learned: Be patient and gentle with yourself and others, if one is sick, and/or experiencing the loss of access to one's mind. Be brave in looking within, to see what you can still do, to change how things are in your life, to find better ways of doing things. If you still forget old stuff, find new stuff that resonates with you now, in the moment. . What are your current Abilities? Work on those, and see where your new path takes you!
It's still all about unconditional love, for yourself, and for others.

My mom was diagnosed around age 72. She passed away a year ago at the age of 81. She ended up in a NH for the last 3 years of her life. While her memory waxed and waned, and on some days over the last 6 months of her life she didn't seem to recognize my brother or me, on her last day she still knew me. She couldn't speak, but she could still mostly understand. The look of relief when I walked into her room told me that she knew who I was. She held my hand for support and they were able to make her comfortable. I talked to her, told her her life story- which she had always loved to hear- and assured her I would be okay. Not everyone with a diagnosis of dementia forgets it all.

Rick, "they" like to reduce everything to simple equations. The mind, however, is complex beyond all human comprehension. You are aware that all is not well, but you still have the ability to think and reason, therefore you are able to pursue any avenue of healing that holds promise. Meditation, prayer, diet, exercise, herbs, physical therapy, or whatever... anything that helps ease your anxiety and strengthen your cognitive abilities.

I've been talking to someone who takes a jellyfish based product called Prevagen to deal with "brain fog" and memory issues. She claims it has helped her greatly, but she doesn't have dementia, just "why did I come into this room?" syndrome that is so common among middle-aged and older. The FDA is not so sure, but they haven't pulled it from the market, and anyway I don't trust government alphabet agencies, especially one that is in the hip pocket of the pharmaceutical industry!

Since I haven't seen reports of side effects, this could be something that might help stave off the progression of your illness. As we all discover sooner or later, even a few extra years of good living is priceless!

P.S. Judging from your writing, I'd say you have better mental faculties than 90% of the people who post comments in places like youtube, LOL!