I want to describe the event of eating pizza, which took place in the past, looking at it back from the present.
Unless you put it in a very unusual context, that description matches the idea of perfective very well.
pIj pItSa' vISoppu'
I've often eaten pizza
(here the aspect {-pu'} is used)
The perfective doesn't come from the adverbial. It comes from the idea of an event of eating.
roD pItSa' vISop
Customarily/habitually/regularly I've eaten pizza
(here the aspect {-pu'} isn't used)
The lack of perfective doesn't come from the adverbial. It comes from the idea of a tendency to eat pizza, or of an assertion that eating pizza is something that happens.
Now, suppose we want to say "in the past, sometimes/occasionally I've eaten pizza", and we're looking back on the event. Do we need to use the {-pu'} here?
rut pItSa' vISop
rut pItSa' vISoppu'
Which would be the correct choice?
The correct choice would depend on whether you mean "I eat pizza" as an event of eating pizza (perfective) or as a general statement of what you eat (not perfective).
And if we want to say "in the past, usually I've eaten pizza", and we're looking back on the event, do we use {-pu'}?
motlh pItSa' vISop
motlh pItSa' vISoppu'
Which would be the correct choice?
The correct choice would depend on whether you mean "I eat pizza" as an event of eating pizza (perfective) or as a general statement of what you eat (not perfective).
Incidentally, none of your Klingon sentences imply "in the past".
-- ghunchu'wI'