"SIDpu' toDta' Qel."
Translation:The doctor has saved the patients.
Is there a reason why the -ta' suffix has to be translated with "has..-ed?" wouldn't the past tense of the verb be enough to indicate the progressive perfective in Klingon? I see no relevant difference between "the doctor saved the patients" and "the doctor HAS saved the patients" when translating this sentence. Some insight would be nice; maybe I'm not understanding something correctly again :/
In most situations you would be correct. You seem to have a correct concept of the difference between perfective aspect and perfect tenses. Because of how the Duolingo course is designed, in this course we ask for the -pu' and -ta' suffixes to be translated by the use of "have/had/will have" in a perfect tense.