entries in the Typo glossary. So you would have to add nx->normal and sep->September into your Typo glossary.
As for the L3-L4 you should get it by typing l3dashl4space as l4 is also in the Typo glossary.
When you type a string like "mid" the dash does not trigger an expansion in your regular glossary for the reasons Emmanuel explained.
Now if you want to get an expansion right after "mid-" you need to press the Escape key to reset the context so Instant Text knows you are starting a new short form. As long as you haven't typed a space the reset is not done, but you don't want the space. That's why you have to use the Escape key.