Here\'s the answer to the question you are really asking:
>So this leads back to my question "Applying the temperature now to convert a volume of fuel pumped 10 hours or 10 days ago will not necessarily result in the correct weight now, right?" It doesn't look like anyone has an experience where weight was mistaken because of a temperature change converting gallons to pounds. And it may be the 3% or so difference has been too small to be an issue.<
Here is the explanation for you (and before we start, understand that I'm not a mechanic or an engineer, so don't nitpick the theory, about which I could care less; I know how the system works from a pilot perspective, and that's what I'm going to tell you now):
Turbine aircraft (at least all the ones which I have flown) employ a fuel quantity measuring system based on measurement of capacitance; that is, electron flow between two charged plates. The beauty of the capacitance system is this: as the density of the fuel increases (i.e., as its temperature goes down) or decreases (i.e., as its temperature goes up), the capacitance of the liquid changes, thus yielding a measure of the fuel's density. The system also uses a known, or reference electrical signal and a sending unit to very accurately measure the level of the fuel in the tank, i.e., the fuel volume. The whole gizmo also incorporates an analog computer unit that uses inputs of 1) volume and 2) density, to arrive at fuel weight, which is presented on the fuel gauges. If memory serves me, the spec for capacitance measuring systems is plus or minus 3%, which is a lot more accurate than the float type gauges in most GA aircraft.
This is why you can fuel up a turbine airplane partially when the OAT is 0 C...let's say, 1/2 full, and the gauges will tell you you have X pounds. If the aircraft sits there until the temperature rises to 35 C, and long enough for the fuel to reach that same 35 C OAT, the gauges will still read X pounds.
This is because (to review), the capacitors of the system measure the decreased density (pounds per gallon) and the reference (fuel level/volume) unit of the system measures the increase in volume due to heat expansion. decreased density X increased volume = same amount of fuel; that is, same weight of fuel. Remember that the amount of matter is measured by the quantity we call "mass," and that equal masses of things at the same location in the earth's gravitational field will have equal weights.
All fuel delivery gizmos, be they updraft carburetors in a Cessna 172, fuel injectors in a Navajo, or fuel control units in a Rolls Royce RB211 high-bypass fanjet engine, deliver fuel by mass, not by volume, in order to achieve a given combustion ration, i.e., ratio of air to fuel by mass, not volume.
The mechanics of how they do this are frankly beyond me, and just as frankly, I know enough about it to get my job done. It's enough for me to know what I have told you, and unless you want to design the things (i.e., be an engineer) or fix them (i.e., be a mechanic), that's enough for you to know as well.