I have two different versions of sentences and want to know which one is right? I have a feeling that both are right. If that is so, tell me which one is more preferable.

1) I was President of Jim Doe Company. I am Presdent of Jim Doe Company, and I will be President of Jim Doe Company.

2) I was the President of Jim Doe Company. I am the President of Jim Doe Company, and I will be the President of Jim Doe Company.

I know you have covered this area of grammar extensively in the past, kindly refer to me the threads if you feel that will serve me right.

Also, am I right on saying that a comma between sentences will be correct to be placed if the sentences are independent in nature and can function on their own, no matter how close they are in content?
Both versions are fine: the first uses the job title and the second uses the position. I am unclear about your question regarding commas, but commas would be preferable to periods here; as independent sentences the style is oversimple.
I believe the second one is correct.. "the president" and not just "president".
And one more thing.. if that is one sentence.. why do you repeat the phrase "the president of jim doe company " ??
Why cant you just put it as " I was, am and will be the president of Jim Doe Company" ??
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Thank you.

I was writing out separately because I was consciously trying to ask about the uses of the phrases or words in each individual context. I am sure your sentence will be the one almost everyone will use when trying to combine those three sentences.
perhaps. . .
"the president" and "President"
The word doesn't need to be capitalized all the time. Like a previous poster stated, one is the title (President) and the other is the position (the president).
Thank you.

When you are writing something using the word in the context of the position, can we write that word (ie, the president) in small letters all the time? Any exceptions where it would be written with the first letter of it in a capital letter (eg, the President)?

Also, can we always use the title with the name to refer to a person in that title?

Do you know Pastor Smith?

Do you know Teacher Doe?

Did you meet Babysittter Kim?

Where is the honorable Judge Chin?

Where is Cook Jinching?
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Re your first question, I am sure there are exceptions.

Re your second question, English uses few of those 'titles'-- only Pastor Smith and The Honorable Judge Chin are natural.
Thank you.

How about in the sentential context below, would you say that the phrase "the district attorney Ron Carver" should be written as "the district attorney named Ron Carver" to be better?

Vance, 45, playes the district attorney Ron Carver in the NBC show "Law & Order: Criminal Internt ."

Also, can I use the colored word as the adjective of the word "sentence"? I couldn''t find that word in the dictionary though.
1-- No; but I might place it into apposition by inserting a comma after attorney.

2-- From Merriam-Webster's online:

Main Entry: sen·ten·tial
Pronunciation: sen-'ten(t)-sh&l
Function: adjective
1 : of or relating to a sentence <a relative clause with a sentential antecedent>
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