I migrated to the new SmartThings App last month and just realized that I did not have a way to manage door codes. I just found and installed the Guest Access SmartApp. It brought over the old codes, but not names. No big deal, I just renamed each code. However one thing that is missing is, I can’t see the code for a specific user.
Any assistance would be greatly appreciated.
Unfortunately as you have already discovered… it is not possible to view the codes through the smart lock guest access. You may want to contact ST support and ask they consider adding that feature 
One option would be to remove all the codes and add them back with names and their respective codes.
Another option is to consider an alternative smartapp…
Has this been addressed? Need to view some old codes to see who they might have belonged to.
What about temp codes or during a certain time frame?
If you’re looking for usage history you may find that within SmartLock.
If you’re looking to see which codes are programmed on the lock then you try the new driver here: [RELEASE] Universal Enhanced Z-Wave Lock Driver for Schlage, Yale, Kwikset, IDLock, Popp, Danalock, August Pro, Keywe, Philia, Samsung
This works with most locks and will show you the programed codes for each slot (it can read them back from the lock now). Note: The only exception here are Schalge locks, you need a Z-Wave plus module for Schlage locks to read back the codes and show them on the device page with this driver.
Thanks Brother! Good to see that you are still around!