Regarding `grid` as an input parameter in 
```c++
BlackoilPropertiesFromDeck::BlackoilPropertiesFromDeck()
```
>> We need the active-to-global cell mapping to extract the correct permeability and porosity values from the input deck.
>
> in this method it's obviously not used, though...

I don't understand what you mean.  Would you care to clarify?  The `grid` is absolutely used within the constructor.  It is, for instance, *explicitly* passed into `rock_.init()` as a (required) parameter if `init_rock` is `true` (default setting).