저는 진짜 한국사람인 만큼...
as I am a native speaker korean...
그냥 간단히 얘기해서,
I must simply say,
알다, 모르다 are original verbs.
so you would not say or use them often.
they are just descriptive words. not for speaking. never using for speaking.
even you never say it in a book by written korean.
I think, only you can see them in a korean dictionary.
알았어, 알았다, 알겠어, 알겠다 are the same meaning.
몰라, 모르겠다 are the same meaning.
I don't know the difference of between them. and No Need to knowing the difference.
If i try, can make the difference but I'm not sure that's correct meaning in Korean grammar.
and also I'm very very sure 99.9999%, they are the same meaning. If someone use them differently with one's exact intention, the meaning only accepted, is just "OK, I see, I got it".
What's the differences of "OK, I see, I got it"? ^^;
So, that's why I simply suggest you, that they are just the same meaning.
even if there is a different nuance, It would depend on that how listener feeling when listener hear the word.
also, the nuance more depending how you sound or how you are saying with some intonation.