clarification needed in a case of 'constraint of a rule' vs 'refinement of an action' ?

I beg to seek a clarification regarding
How do we decide in some cases to choose between
'a constraint to a rule' vs 'refinement of an action' ?

------------------------

Let us consider the example 13 in
https://www.w3.org/TR/odrl-model/#constraint-rule

(A)

{
    "@context": "http://www.w3.org/ns/odrl.jsonld",
    "@type": "Offer",
    "uid": "http://example.com/policy:6163",
    "profile": "http://example.com/odrl:profile:10",
    "permission": [{
       "target": "http://example.com/document:1234",
       "assigner": "http://example.com/org:616",
       "action": "distribute",
       "constraint": [{
           "leftOperand": "dateTime",
           "operator": "lt",
           "rightOperand":  { "@value": "2018-01-01", "@type": "xsd:date" }
       }]
   }]
}

------------------------

what would be the reason that prevents us from expressing the same thing as

(B)

{
    "@context": "http://www.w3.org/ns/odrl.jsonld",
    "@type": "Offer",
    "uid": "http://example.com/policy:6163",
    "profile": "http://example.com/odrl:profile:10",
    "permission": [{
       "target": "http://example.com/document:1234",
       "assigner": "http://example.com/org:616",
       "action": [{
          "rdf:value": { "@id": "odrl:distribute" },
          "refinement": [{
              "leftOperand": "dateTime",
              "operator": "lt",
              "rightOperand":  { "@value": "2018-01-01", "@type":
"xsd:date" }
          }]
       }]
   }]
}

thanks and regards

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