In EDC15 the specified MAF is 100% about the EGR. Nothing more, nothing less
In newer models the MAF is used for other things, but it's still mostly about the EGR. Keep in mind, the airmass entering the intake manifold is not equal to the airflow at the maf.
manifold = maf + EGR
through experimentation on a test stand, The factory knows how much airflow the engine consumes without a maf. What you see in VCDS is the outside air being consumed WITH egr flow lowering the outside air requirement. So in other words, the maf reading is:
MAF = manifold - EGR
Maf is not equal to the total quantity of gas being consumed by the engine at any one time. It is equal to the total consumption of the engine minus the egr contribution to the consumption.
The EGR rate needed for emissions certification is found by experimentation under standard conditions on a test stand (engine dyno). Then they empirically measure the MAF airflow under the prescribed egr rates. a bunch of times, under a number of operating rpm and load conditions in this controlled laboratory environment, to come up with an "average" for each load and rpm. This data is processed into a basic setpoint map (basis map) inside the ecu. Then some environmental variables are changed in a controlled way, and the airflow changes measured. These environmental effects are programmed into other (complimentary) ecu maps which are used as modifying variables, to "educate" the setpoint under various environmental conditions. (essentially creating a dynamic, "virtual" setpoint map at runtime) The goal here is to keep emissions compliance in almost any conceivable environmental condition, since the cars will be driven in a variety of weather and altitude. Both the setpoints maps and duty cycle maps are dynamically generated this way at runtime, however...
Certain operating conditions have the ecu in closed loop mode (feedback, or regulating, or governor if you will) and others have the ecu in open loop mode (feedforward, or steering mode). Closed loop uses all the modifying factors and feeds the data in to a PID controller to actively regulate the EGR valve duty cycle based on the calculated desired flow at the maf, to achieve the desired egr rate. Open loop ignores the actual maf and simply follows the egr duty cycle basis map to control the egr without looking at what's actually happening at the MAF. there is another set of maps and setpoints to tell the ecu when to use each feedback mode for the particular parameter being controlled. (note: this schema applies to just about everything that's ecu controlled, such as boost, fuel, timing, cruise control, etc, only different in the variables being montiored/controlled and the inputs/outputs. this is how the factory (and good aftermarket tuning) tunes cars to operate reliably and consistently under all environmental and altitude conditions)
What you see in VCDS as the "specified" is the airflow value being used to control the EGR, however it's derived. You also see the egr valve duty cycle, though you won't be able to tell in vcds whether it's open or closed loop mode.
I get calls sometimes from guys who are worried to death that their MAF is reading higher or lower than specified. I usually get the call after their mechanics go to great lengths to try and get actual and specified to match. I end up having to explain why this is not a concern. The "specified" is only a crude estimate of what the MAF airflow should generally look like with the egr exactly like the engine on the test stand. There is a fairly wide tolerance band, something like 125 or 200 mg/r plus or minus, depending on the exact model of ecu. If you unplug the egr, you will see the actual maf and specified maf will not match at any time. My point here is, just keep in mind there's a wide tolerance allowed by the factory and it only relates to how much egr flow. I know VCDS shows actual/requested maf air flow, but please realize this maf flow actual/requested comparison is only intended to give the ecu some rough idea of how to adjust the egr valve duty cycle. Nothing more, nothing less. (yes, I know the maf actual MAF value is used for other things but I'm only talking about the actual/specified comparison here)
It's not about what the engine "needs", it's about the EGR, and that's all. I think a lot of mechanics are still in gasser-think mode and don't understand that diesels don't care about stoichiometric air to fuel ratios. In a gas car, if you run too lean, you will burn up the valves or worse. So the correct a/f ratio is very important in a gasser. In a diesel, too lean is "just right". So drive more, worry less.