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Please tell which you believe to be the best. The words in bold are words I added in attempt to make the sentence clear.

Original: Additionally, I understand the importance of such relationships, having worked in companies such as X and Y in which 20% of the customers create 80% of the revenue.

Edited #1: Additionally, I understand the importance of such relationships. I worked in companies such as X and Y in which strong relationships were of the utmost importantance, as 20% of their customers created 80% of their revenues.

Edited #2: Additionally, I understand the importance of such relationships, having worked in companies such as X and Y in which strong relationships were of the utmost importance, as 20% of their customers created 80% of their revenues.

Edited #3: Additionally, I understand the importance of such relationships. I worked in companies such as X and Y in which strong relationships were of the utmost importance, as 20% of the customers created 80% of the revenues.

Edited #4: Additionally, I understand the importance of such relationships. I worked in companies such as X and Y in which strong relationships were of the utmost importance and in which 20% of the customers created 80% of the revenues.

Thank you
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I suggest this:

I understand the importance of such relationships. I have worked in companies such as X and Y in which strong relationships were of the utmost importance: 20% of their customers create 80% of their revenues.
Comments  
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Mister Micawber
I suggest this:

I understand the importance of such relationships. I have worked in companies such as X and Y in which strong relationships were of the utmost importance: 20% of their customers create 80% of their revenues.


Yours is much clearer, thank you. However, splitting the first sentence into two means there is no subordinate clause showing the relationship between the two clauses (why you understand the importance). Does this not matter? Is the link between the clauses so obvious that they don't need to be joined?
Yes, the connection is obvious. Start thinking semantically and stop worrying so much about punctuation.
Mister Micawberstop worrying so much about punctuation.

Hi,

I wasn't worrying about punctuation. I was worrying about the relationship that may be lost from changing a subordinate clause of reason to a main clause.
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