To ensure that the mailroom does not erroneously reject your non-subject H-1B, make sure the cover letter emphasizes in Bold, 14 point font, colors, etc., that the petition is NOT subject to the cap. Make clear why the petition is not subject to the cap, and state it as simply as possible. In addition, double check that the correct H-1B petition type is indicated on the certified LCA and all accompanying documentation (be consistent!).
Also, remember that when filing H-1B extensions for the same employer, the $500 fraud prevention fee does not need to be paid. Make sure to highlight this in your cover letter to avoid rejections. Provide proof of the prior H-1B petition approved on the beneficiary’s behalf by the same petitioner, highlight the petitioner and beneficiaries’ names, highlight the instructions to the form I-129, indicating that such fee is not required, and provide a statement (in bold) stating why the $500 fee does not apply. Taking such steps will definitely minimize the chances of such filing being rejected.