4 points
I had a think about this scenario and I think that if Steam was going to present this argument they would need to document and support this workflow. At the moment the fact that it sometimes works is more of an accident than anything (essentially it’s all just files on a disc and sometimes the files still work if you move them somewhere else).
But if they document that you can transfer the install data to another location, and identify which titles that applies to? Then I can see a reasonable argument that they qualify.