@debbraw - Good questions! The "milestones" of progression from MCI to dementia can be subtle from day to day, so you are spot on in your analogy of this being like the aging process. For healthcare providers, who see the patient every 6 months or every year, changes appear a bit more pronounced. What many of us tend to hone in on is how the person is functioning in daily life. Usually, when MCI progresses, we hear about a patient having had some mishaps with medication management, bill paying, cooking, or driving tasks, to the point that family members have stepped in and taken over some or all of those things. Essentially, that loss of function is a symptom of cognitive difficulties getting worse, with progression of the underlying disease. You are also right that dementia has stages (mild, moderate, severe). I'd suggest taking a look at the Alzheimer's Association website resources for more info on that (https://www.alz.org/alzheimers-dementia/stages).

The important thing to remember is that the progression is not always consistent so some days go better than others. It is a full time job to remain calm and not argue with their "facts." It is important to protect yourself, especially when they drive. It is important to get control of the money needed to get through the coming years. Don't wait. In the beginning, take every strange event seriously. Do not believe the lies they tell to cover up their foggy brains. They know their is a problem but they are in denial or they believe it doesn't matter.
Dorisena

I noticed something missing from the discussion on gradual decline that I observed in my life. If a male spouse doesn't do many of the daily independent actions for years on end because his spouse does it for him, he naturally declines in that area, under the idea that if you snooze, you lose the ability. In other words, having a servant at the meal table means you learn, or forget to do many actions for your self. My husband's grandmother served him standing up during a meal, as was her cultural custom, and she ate later in the kitchen. For fifty years my husband never thought to rise and get a missing bottle of ketchup for his use, and all condiments on the table had to be passed to him, as he never learned the initiative to reach for anything himself. He was served, like a King! After forty years of marriage I announced at the table of six people that I had worked hard on the dinner, and if anything was missing or they needed anything extra, they should get it themselves so I could sit and eat with them at the table. My husband never complied. He sulked and I ignored it.
At that point if I left him or died he would not be able to feed himself and my family realized we had a problem for the future. Was it MCI or poor training? Was it power play, stubbornness, or expecting a slave mentality from the spouse? Or was it MCI? He quit using soap in the shower. He never turned off a light switch. He became a burden to everyone to live with. Eventually it became dementia.
Dorisena