In the published materials, Tolkien doesn’t say anything about the Adûnaic continuative past other than that it exists. Its function is unclear, perhaps indicating that action was one that was ongoing in the past. There is only one example that seems to be a candidate for this verb tense, as noted by several authors (VSH/28, AL/Adûnaic, LGtAG):

• Ar-Pharazônun azaggara Avalôiyada “Ar-Pharazôn was warring against the Powers”

Unfortunately, this verb’s form changed in each version of the Lament of Akallabêth: azgaranādu (first draft) >> azagrāra (second draft) >> azaggara (final draft). Each of these forms seem to be some conjugation of the derived verb azgarâ- (SD/439), but there is so much variation that it is hard to tell the purpose of the changes. Even worse, there are no other attested conjugations of derived verbs, making comparisons to other verb tenses impossible.

Most authors note the similarity of the form azaggara to other double-consonant (geminate) forms in the Lament. Carl Hostetter and Patrick Wynne went so far as to conclude that all of such forms are the continuative past (VSH/27-29). Most other authors have suggested (AL/Adûnaic, LGtAG, NBA/26) the other geminate forms are more likely to be the Adûnaic past tense, something with which I agree. Thorsten Renk furthermore suggested (NBA/14) that the final verb form azaggara may actually be the ordinary past tense of azgarâ-. This also seems plausible to me, though it is hard to explain why Tolkien didn’t change the gloss from “was warring”.

If this reasoning is correct, the second draft form azagrāra may be the only true example of the continuative past, but this is all so speculative that I wouldn’t try to make a rule out of it. The fact of the matter is that there isn’t enough evidence for the Adûnaic continuative past to figure out how it was formed or how it was used.

Draft Verb Conjugations

The attested example in the draft of the Lament, azgaranādu, bears little resemblence to any other attested Adûnaic verb conjugations, making it very difficult to analyze. Carl Hostetter and Patrick Wynne very tentatively suggested (VSH/35) that the -d- might have been the marker of continuity at this stage, but admit that this pure speculation.