Strange messages from fsck_hfs
The command you have given includes the "-l" option, which means to perform a "test-only check" and that "no repairs can be made". Essentially this means that it won't write to the file system, which explains your questions 1 and 4.

Regarding questions 2 and 3: The disk as such might be "OK" (i.e. usable) from the point of view of the filesystem even though a single bad block has been detected. As you have specified the "-S" option, fsck_hfs will attempt to match the bad block to a file name - it found not match. This could indicate that the bad block does not affect any of your files.

Consider replacing the drive when you start having bad blocks.