How to get value of customer property linked to another file

I have a drawing file linked to a model with custom properties like: \$PRPSHEET:"Revision". Problem is following:

a) Even in the custom property list the value is not calculated (the resolved value is calculated for some of the properties, but not for those references to another file - so in the "resolved value" column there is also \$PRPSHEET:"Revision", not the actual number)

b) I need to get this value (computed) in a macro - but when I call

swCustProp.Get4("Property_Name", False, val, valout)

then the val and valout both return just \$PRPSHEET:"Revision" as a value - not the actual revision no.

Am I doing anything wrong? Or how can I get the real property value?

SolidworksGeneral