[O_H_E]

Does that refers for the months of March and April???

[rgoulter]

Jan -> January, Feb -> February; Mar -> ... Frequently used parts of language are often irregular. Fortunately, I don't think plaintext you'd use sed against is as irregular.

[O_H_E]

Well, I understand this comment, but your original is still unclear to me. You might want to clarify it for others.