All of the following assumes that you are playing the new-formats version of NepsterLems.
1) Your second message is correct. If you don't save even half of the required lemmings, then it should display the "Rock bottom" message.
2) The first one is indeed incorrect. The reason lies in the text file specifying these messages. Turns out, the order of the messages in this text file is important
: It has to start with the least successful message and go on until finishing with the most successful one.
3) This is actually a bug in the new pack toolkit, too. The next version will write the "postview.nxmi" file correctly.