On average this doesn’t matter. Humans are a whole lot more predictable and pattern based than you seem to be implying.

Also, if you’re trying to aim to a specific deficit, you should be calorie counting your food. If you got fatty dressing, you should be counting that. Even estimating is relatively easy once you do it for awhile. And if you don’t get it quite right, being a little off shouldn’t impact your overall average too much. It keeps you honest, which I think is by and large the main reason people don’t think they can lose weight: dishonest assessments of food consumption.

As I've said, I can absolutley lose weight, but I cannot reliably lose one pound per week; I do not seem to have that resolution in the numbers.

I've been tracking my weight weekly and all calories (even with crude estimates in some cases) for a year and a half, and have been experimenting with exactly this: I made a scatter plot and linear regression of average calories per day on the X axis, and weight change for that week on the Y axis.

Week to week weight has extra fluctuations that make it difficult to tell what's going on, but after around 6 months of data it stabilizes, and has been consistent for any 6-month period over the last year and a half: I burn around 2200 - 2300 calories per day on average (way higher than the online estimator tools think I burn, 1600 - 1700).

Knowing this I've also been reliably able to control my weight up or down at the rate I want as long as I'm looking at it for over a month span - because as above, week to week there's too much fluctuation (fullness of stomach and bowels mostly).

That it takes that much data to see the result pretty much proves my point - maintaining a 500 calorie per day deficit is just very difficult for me and I suspect most people. I don’t mean the hunger - when I do lose weight the deficits are easily above 1000, but 500 is too marginal for me to resolve.

Reliably losing one pound a week (beyond the initial 1-2 week period where your weight is going to go all over the place due to water weight fluctuations) is as simple as cutting calories until you see the weight (on average, ignore fluctuations) drop by 1 lb a week. You have to average extensively. Bodies are very temperamental at this, unfortunately. My scale weight swings 0.5-1 lb quite frequently mainly due to sodium changes in my diet. It’s all about trend weight, though.