I think I have it all figured out, and it's very discouraging.
Prelude: all my investment income is recorded as downloaded from Figelity, Schwab, Vanguard, and Franklin Templeton. That was what I meant when I said they were mostly DivX transactions (dividend paid to a brokerage account, transferred to an account holding a money market fund.
The Estimated Income column in the portfolio screen comes from only one place: the estimated income parameter in the security edit screen (second page or more advanced options). This is (I tried it) the expected annual income per share. That means that Quicken is merely spitting the information back to you, and when the dividend rate changes you need to edit the security definition sheet if you want anything meaningful to appear in the Portfolio screen.
So Quicken is not calculating dividends received and extrapolating them to a full year, it is simply multiplying two numbers together. Not particularly helpful, is it? I do better than that with my Excel dividends spreadsheet, where I extrapolate projected annual dividends by taking the sum of the dividends-to-date and adding to it the maximum dividends-to-date multiplied by the nmber of remaining dividends to be paid. Since it is December I have added an earnings-per-share column to my spreadsheet (projected annual dividends divided by number of shares). I fortunately can avoid the complications of reinvesting dividends because I take all my dividends as cash income.
Just a footnote: it is necessary to know for each security the total number of dividends per year, because I own two mutual finds for which the number is not 12, not 4.