1. If I'm narrating events of the past using "historical present", i.e. describing them as they happen, then no perfective is used.
2. If I'm looking back from the present on actions performed and completed, then I use perfective.
3. If I'm looking back from the present on habitual events/actions of the past, events which can be described by the "used to", no perfective is used.
4. If I'm looking back from the present on completed events/actions of the past, which weren't habitual, but happened more than once, perfective is used:
5. If I'm looking back from the present on quality verbs, and the quality described can be described by the "used to", no perfective is used:
All good. I don't think I'd personally split them up this way,
but I don't disagree with anything here.
6. If I'm looking back from the present on quality verbs, but the quality described can't be described by the "used to", perfective is used:
In the past the water has been hot
In the past there was just one (or maybe two/three/more) occasion(s) when the water was hot
(the second sentence describes the intended meaning)
pa'logh tujpu' bIQ
In the past the water often has been hotpa'logh pIj tujpu' bIQ
This is the best I can do when it comes to understanding the {-pu'}, and I'd love to hear whether you agree/disagree with the above.
This one I don't agree with. The words used to aren't necessary to avoid perfective; they're just a convenient, but incomplete, test to see if you're thinking in terms of perfective or not. Besides, I don't see why the water has often been hot couldn't be said as the water often used to be hot. So I don't think you're looking at used to in quite the right way.
I wouldn't use perfective on either of these. Even if you're describing water that was only hot two or three times, you're still describing the being hot, not a completed action of being hot. 'op ret tuj bIQ in the past, the water has been hot; 'op ret pIj tuj bIQ in the past, the water has often been hot. Putting the English translations into the present perfect tense is a feature of English, not Klingon. Klingon doesn't mark verbs for "past action that is relevant now" the way English present perfect does. You could just as easily translate these 'op ret tuj bIQ in the past, the water was hot and 'op ret pIj tuj bIQ in the past, the water was often hot and still have a perfectly correct translation. The concept of "past action, relevant now" doesn't exist in the Klingon original.
(By the way, I believe pa'logh refers to the past as a
whole, not to some point in the past, which is 'op ret. To
refer to some action taking place at the time pa'logh
makes very little sense, as if the whole of the past was just one
little dot on a timeline.)
-- SuStel http://trimboli.name