I learned that ている can be used in both Continuous Tense and Perfect Tense, and with both instant state change verbs and durative verbs. If we consider only durative verbs (e.g. 食べる, 作る etc.)
When is ている interpreted as Perfect Tense, and when does it mean Continuous Tense? Let us say, my mom asks me, お祖母さんが食べたか？ If I answer お祖母さんが食べています it can mean, both "My grandmother has eaten the food", and "My grandmother is eating the food". However, what I want to imply by using ている is that she has eaten the food i.e. to use the perfect tense.
A different example:
ている seems to mean either continuous or perfect tense, and the English translation provided by the dialogue creator is perfect i.e. "I have made 20 cookies."
When should ている with durative/action verbs be taken as perfect tense and when as a continuous tense? Could you please give me some practical examples and tips that I could use to differentiate?
Do native Japanese speakers usually interpret ている with action/durative verbs like 食べる, 作る, in perfect tense or as continuous?
Two adverbs まだ and もう also seem to be used in perfect aspect. もう leans towards a positive perfect tense reading, when used with a verb in the past tense (た）e.g. もう食べた (I have eaten), and まだ usually points to negative perfect tense with ていません e.g. まだ食べていません (I have not eaten). Also ~ことがある. So, my third question is, whether the one of/sole purpose of using adverbs もう and まだ, is to remove the conflict, and confusion, arising because of durative/action verbs having two tenses when using ている? E.g. does the use of もう食べた, instead of plain 食べています (which also has the same perfect meaning) to remove the confusion, when the person wants to tell his state that he has eaten the food?