Don't know what phones were in use, but 'the network' would surely have a record of what was going on at the time.
That's my point - I don't think it would. If you are composing a text on your mobile, the network knows nothing about it while it's a draft, only after you have hit Send.
I'm not implying that's what happened, simply that it's a possible scenario.
According to the SB, there was a message received but 'not read'. Thats not to say that it wasn't seen.
Actually, I think that's exactly what it does imply.