You need to control which -compareto operator to use in different situations.
In previous posts, you mentioned trying to determine the changes in a GETLABEL vs. the repository, so your choice of compareto of 'lastget' works here.
In the last post, "I did a GetLatest on test.txt to the workingfolder". Were there any changes made to the working folder copy? The compareto option using 'lastget' will show differences in the working folder copy and the file at the time of the last GET. Since nothing has changed in the working folder copy, there will be no differences. You could try using compareto of 'current' in this case.
Also, from this link
http://download.sourcegear.com/misc/vau ... c.htm#DIFF (or running "vault.exe help diff" from the command line) you can see all of the options for '-compareto'. In regards to the initial posts to this thread, have you investigated using the 'label' compareto option?