Partly Baked Idea [terminology due to I J Good]:
I suggest splitting the current Guest/Practice no-password login
Each of the following would be able to view a problem set without password and no "Submit Answer" button. Option to view Hint but no ability to view Solution (even after closing date) and with no answers retained between sessions.
Practice --- audience: students in current/related class
Check Answer button (in addition to Preview Answer)
create a fresh version (i.e., reseed)
option to display previous answers during this session
Observer --- audience: teachers
Check Answer (in addition to Preview Answer)
fresh version (reseed)
Display Code button (also show path in NPL or wherever)
Guest/Visitor = current level, i.e. -5 access (perhaps escalate to -10 ;-)
Some reported difficulties involving inadvertent use of Guest login by current students might be inhibited if its display had a distinctive coloration --- e.g., use a yellow or light green background, perhaps with a preliminary page announcing that subsequent work with this anonymous access would not be recorded.
I see no situation where all of these would be enabled.
The MAA or MathObjects tutorial might have Observer active while my current Precalculus or Calculus class might have Practice turned on.