The "NotReady" codes don't appear to be documented anywhere, but they have important info. I don't know if these are some binary code like the flags are, but I have found:
7 - bin missing
15 - (is possibly) low battery
16 - bin full
It's interesting that when the bin is full, Roomba just goes and parks itself without giving a warning. Seems like a design flaw (that I have now fixed by sending a message when that happens).