The data card is the spec from the factory, when you add extras each item has a factory code and at Mercedes is can be added, it does show as an extra but when you quote your reg number for parts etc the right ones will be found, so for instance if you changed your windscreen for auto lights type and did not up date the data card next time you need a screen the wrong type would be supplied.
Also it has data that modules in the van needs for items to work or even see and without SCN coding it will not work.
What condition is your screen, any chips? its not going to be cheap but well worth it, the overhead control is used, the rest all new.