It matters in two cases below:
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TN 工作結束時, 開車離開美國, 但美國CBP website上的 I94卡上沒有出境記錄, 美國CBP認為我非法滯留美國. 將來有麻煩.-In your case, you will reenter US and thus, you will get the new I-94 arrival record (the status record will be re-counted). So, you don't have 非法滯留美國 problem.
- 報稅要用在美國的天數. 並且要填寫出入美國日期. 但CBP website上 的出入美國日期錯了. 美國認為我造假.-You have worked in US and got the salary, so you have to pay the tax no matter how long you stay in US. Why do you care about a few days of stay outside US? Don't think you can save significant money by just not ocunting the days you are out of US.