Stage and state need more work
I'll discuss stage first, and then discuss state in a separate comment below.
The object property stage is applied to a vf:EconomicResource and references a vf:ProcessSpecification.
Its description says
References the ProcessSpecification of the last process the economic resource went through. Stage is used when the last process is important for finding proper resources, such as where the publishing process wants only documents that have gone through the editing process.
The property stage was motivated by use cases where the same EconomicResource is both an input to and output from a process; especially when the same resource goes through a series of processes.
Common examples include bread dough, which can go through several stages of mixing, rising, and kneading until it is ready to bake. Another example is document translations, as mentioned in the stage description, which can go through several stages of translation, proofreading, editing, and preparing for publication.
What I think is missing is any way in VF to specify which stage is required for an particular process, for example, to specify that "the publishing process wants only documents that have gone through the editing process".
The logic of stages was prototyped in NRP, aka ValueNetwork software, where the specification of what stage of a resource is wanted by a particular process was implemented in the NRP equivalents of input vf:RecipeFlow and vf:Commitment as an input to a vf:Process.
Stage was used in generating plans from recipes, in the netting method, where the plan generation looks for existing resources that can satisfy an input requirement, and also in selection lists in forms for entering which resources were the actual inputs to a process, so that if a particular stage was required, only resources with that stage would be selected.
But neither vf:RecipeFlow nor vf:Commitment have a stage property. I think those would be the appropriate places to specify what resource stage is wanted by a process, but they can't do it, as far as I can tell.