I've assigned Issue 18 to the question of whether it is
permitted to use 1yz codes without extensions and whether
additional text is needed to clarify the answer (whatever it is).
It appears that there are four options:
(i) Do nothing, leaving the text as is
(ii) Make it clear that 1yz codes are prohibited without
extensions.
(iii) Specify conditions under which a
2821bis-conforming server, without extensions, may
generate a 1yz code and what clients are expected to do
when such codes are received.
(iv) Say nothing more about servers generating these
codes, but offer some guidance to clients if they
receive them (whether the server is otherwise conformant
or not).
john