I happened to read the rules section on pg 12 of the ES rulebook. There you find this text:
During the Attack the Ancient One step, players roll dice as they
did during the Resolve an Adventure Card step. Each Ancient
One has a Combat Task printed on its card. Each time the active
investigator completes this task, remove a Doom token from the
Doom track. Investigators may complete the task any number of
times during the Attack the Ancient One step (but only once for
each time they roll the dice).
I highlighted the last bit of this excerpt in order to ask for a rules clarification - let's work with an example:
Let's say you need 1 Peril, 1 Terror and 1 Lore in order to successfully pass a task on an Great Old One while battling him. While you play your attack against this Great Old One you roll all six dice. And your first roll already shows each symbol once. So you would have successfully passed this task during your battle against the Great Old One. You would be allowed to reduce the doom markers on the Great Old One by one. No question about it; no doubts as well (hopefully).
Now the question:
Three of your dice did not do anything to fulfill the task. According to the rule-excerpt mentioned above: Would you be allowed to reroll those three dice after your first successful attempt in order to try to get a second success and therefore in order to draw one additional doom token away from the Great Old One on your current/ same turn? In other words: Would it theoretically be possible for a gamer/ investigator to actually pass the task of most/each Great Old Ones twice on each turn?
I feel inclined to say: Yes. No problem - in theory you are allowed to do so. But am I right with this conclusion?
All the best!