You don't have to explicitly list out all digits, just the ones you want as options off your menu. Set a default and just list out the options that do something else.
1 collect 1 digits after announcement 12345 for none
2 goto step 21 if digits = 1
3 goto step 23 if digits = 2
...
15 # Play "Invalid selection" and repeat menu
16 announcement 12346
17 goto step 1 if unconditionally
...
21 # Option 1
...
23 # Option 2
...
Notice how there are only goto lines for specific digits. In this example, any digit entered that does not have a line defined in steps 4-14 will by default go to the "Invalid Selection" step 15. This also works if the caller selects nothing.