What exactly is in a history line?
Each line shows the time of the missed call, the number and, if the person is in your address book, their name. Then comes what happened to the text: sent, delivered by the carrier, failed, or not sent with a reason. The reasons match the guardrails you set: number on the STOP list, daily cap reached, minimum spacing between two sends, or a number that already received a message today. Withheld numbers are listed too, but without an SMS, since there is no number to reply to.