Where should the parenthesis be placed? By the time he retired in 1991, he had won numerous all-star honors 12. By the time he retired in 1991, (he had won) numerous all-star honors 12. By the time (he retired) in 1991, he had won numerous all-star honors 12. By the time he retired in 1991, he had won numerous all-star honors (12). By the time he retired in 1991, he had won numerous (all-star honors 12).

Parentheses () is a punctuation mark mainly used to add information which usually clarifies some section of the sentence and works as an aside, which means the information that is added does not grammatically belong to the sentence but is somehow independent to it. Additionally to this, a parenthesis can include a word, number, a fragment or even multiple sentences that serve as a comment or clarification of the main sentence. Considering this in the case of the sentence "By the time he retired in 1991, he had won numerous all-star honors 12" the only information that serves as a clarification of the main sentence and does not belong to it grammatically is "12" that serves as a clarification of the number of all-star honours the man being described received, therefore number "12" should be in parentheses, which means the correct sentence is "By the time he retired in 1991, he had won numerous all-star honors (12)".