My question arose when I saw, in Allen and Greenough's New Latin Grammar (1903), p. 311, the statement Gallia est divisa translated as a predicate adjective (Gaul is divided.). I looked briefly at the context of this head statement in Caesar's BELLO GALLICO, and in my opinion (which at my level is of course of very little merit), felt that it just as well could have been translated as a periphrastic perfect passive. I checked with Woodcock's A New Latin Syntax (1959) in section VII 'The Use of Participles,' at p. 79: which provides, in part: "The perfect participle in -tus originally denoted a state, so that Hannibal victus est meant firstly 'Hannibal is beaten' (of a present state). But this, for practical purposes, is equivalent to saying 'Hannibal has been beaten') of an act completed). Thus victus est came to be used as the passive tense-equivalent of vicit, and in both senses of vicit (true perfect, and aorist). Nevertheless victus could still be used as a predicated adjective, so that Hannival (sic) victus est, erat, erit, may mean either 'Hannibal is, was, will be, a beaten man', or 'Hannibal has been, had been, will have been beaten', according to the context."
A&G clearly state in sect. 495, p.313: "Participles are often used as Predicate Adjectives. As such they may be joined to the subject by esse or a copulative verb. ... NOTE. -- From this predicate use arise the compound tenses of the passive, -- the participle of completed action with the incomplete tenses of esse developing the idea of past time, as, interfectus est, he was (or has been) killed, lit. he is having-been-killed (i.e., already slain)."
As a related aside: both of these modern Latin Grammars also recognize the use by Latin authors of the perfect participle with fui, fuisti... fueram, fueras... fuero, fueris....
I find some understanding of the history and evolution of the participle in these Grammars, but not any really helpful guidance or hint on how to translate the construction in this remote and isolated corner of the universe now 2000 some odd years from the time when these statements were uttered. Context is of course helpful evidence, albeit hearsay.