SMS Event Documentation Unclear

Reference: ADL User Guide for Open At v3.03, Rev 001, Dec 2005.

The description of the SMS Event Handler does not explain the distinction between ADL_SMS_EVENT_SENDING_OK and ADL_SMS_EVENT_SENDING_MR.

It says they both mean “SMS Message was sent successfully”, but one has the message reference, and one doesn’t.

In my system, it seems that ADL_SMS_EVENT_SENDING_MR is always received first, followed by ADL_SMS_EVENT_SENDING_OK.

Is there any case when only one could be received, without the other?

Is there any case when they could be received in the other order?