A construction such as huwa musriʿun has an overt subject and predicate and may sound like a newly begun assertion if placed after a sentence without wāw. This possibility underlies the argument that an explicit circumstantial wāw is required when the bearer's pronoun serves as the nominal subject.
But the potential to stand alone is not identical with actually being independent in context. Textual clues, discourse order and established usage can sometimes make the circumstantial reading clear without an overt connector. The debate concerns how far the proposed requirement should extend.