Need this Grammar Explained so I can use it myself.
While reading an email, I came across this sentence:

좀 천천히 찾아보니 제가 몇가지 놓친 부분이 있었던거 같습니다.

I think I understand it to mean "While slowly browsing, I missed a few included parts." The email goes on to call out thing he missed and now understands after reading an article more carefully.

My asks:

1. Please correct my understanding of the sentence if it is not correct.
2. The grammar patterns used in the sentence confuse me because I don't think I've ever used them before, and never had to understand them in depth. Can you please diagram the sentence, and especially with the use of affixes like 던가 so I can make use of these patterns as appropriate in the future.

Thank you.

(Learning in the heat of the situation is how I learn best, but I have to admit, itis stressful in key areas :) ).

Question

Need this Grammar Explained so I can use it myself.
While reading an email, I came across this sentence:

좀 천천히 찾아보니 제가 몇가지 놓친 부분이 있었던거 같습니다.

I think I understand it to mean "While slowly browsing, I missed a few included parts." The email goes on to call out thing he missed and now understands after reading an article more carefully.

My asks:

1. Please correct my understanding of the sentence if it is not correct.
2. The grammar patterns used in the sentence confuse me because I don't think I've ever used them before, and never had to understand them in depth. Can you please diagram the sentence, and especially with the use of affixes like 던가 so I can make use of these patterns as appropriate in the future.

Thank you.

(Learning in the heat of the situation is how I learn best, but I have to admit, itis stressful in key areas :) ).

Answer

1) ~(해) 보니: as a result of (~한 결과)

(ex) 그를 개인적으로 만나보니 - as a result of meeting him in person
           좀 천천히 찾아보니 - as a result of proof reading

2) (있었던 것) 같습니다 : It seems that~

(ex)  제가 몇가지 놓친 부분이 있었던 것 같습니다.
             It seems that I overlooked some parts.
             --- It is a euphemistic phrase than "I overlooked some parts." in Korean.
                     But I think this phrase is wrong in many cases. 
                     For example, "It seems that it is my fault."

Answer

Sorry, I meant 갔다 = "used to go". Isn't that right? 가다 + 았던. I think in English this means "to do something in the past for a while and then it ends". Maybe you didn't complete it. 자주 갔던 식당 = "restaurant I used to go to often". Is that correct?

Answer

I'm sorry, typo. I meant 갔던 = "used to go".

Answer

@Mojave I didn't see your comment before answer. You are right, but I have different view about one thing. You said, "-았/었던'(or just -던)" can be translated to "used to go."
This phrase related to a kind of habit, isn't it? So, I can not translate the original sentence(in Korea) to English by using the phrase "used to go."

Answer

I can explain a few things. 것 같 (거 같습니다 in your sentence) is used to mean "I think that/It seems that". It's used to soften something. For instance, instead of "There was an earthquake", you would say "I think there was an earthquake". -았/었던 or just -던 is more than just the regular past tense. It translates best to "used to + V". 갔던 = used to go. 몇가지 놓친 부분 = some missing parts/things (I think). So I think the second part of the sentence, 제가 몇가지 놓친 부분이 있었던거 같습니다. means "I think there were some parts/things that I missed". Note: I'm learning Korean too, so my explanation may be off a bit. :) We'll see what a native has to say.