I think there is no difference in the above two sentences. 'Clerk concerned' or 'Concerned clerk' are absolutely fine. The mistake may be somewhere else. The correct sentence may be: Please talk to the concerned clerk.



3. Not only he was a thief, but he was also a murderer.
Correct: Not only was he a thief, but also a murderer.
Reason: Not only... but also... are used in combination. Not only is always followed by verb/helping verb. Therefore, 'was' is placed after 'Not only' in this case.

6. My uncle has told me something about it yesterday.
Correct is: My uncle told me something about it yesterday.
Reason: When the words like yesterday, last year (Past time) are used in the sentence, past indefinite tense is used.

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