Fuel Refinery output not correct according to indicated??? Why ???

[quebec.qd]

Can someone try to explain to me why the Fuel Refinery does not produce the amount of fuel as indicated? I drop off 70 Oil and expect the refinery to produce 70 Fuel (this is what the refinery indicates by showing 1 oil needed for 1 fuel).
However, my train drops of 70 oil the first time it gets to the Refinery, and does not load anything. (I was doing a test, so I made sure my train did not load anything. The train leaves and when it comes back, it drops off 70 fuel but only receives 64,65,66 or 67 fuel. Why? Should there not have been 70 fuel waiting?
If this is some kind of loss due to standing time or something like that, then state that somewhere and don't indicate 1 oil gives 1 fuel because it is not true.
Can someone help me understand this please.

I also wish this game had a better manual that explains things like these, so that we don't have to come here to ask a simple question every time and have to wait hoping someone has an answer for you.

The Game Developers should be explaining and answering the questions we have.

[Autocoach]

Hi, the first unit of a fresh production run is always lost so you reduce to 69 if the refinery is working on a stop-go basis rather than constantly . The other issue is fuel is only shipped if there is a customer , maybe visible demand is only 67 and the third issue is a little delay between production and product arriving on a platform.

[Vimpster]

One last consideration is that viable demand is not instantly recognised, but slowly ramps up, so some product could have been processed prior to the full demand being recognised. Any processed cargo without demand never gets created even though the cargo used to make it is consumed. You can click on the fuel refinery and select the consumers tab to see how many customers it is currently recognising.