I-D Actions ?

Dear all.

I've found that there are two cases for ID action issued by IETF,
without regard to the fact that it is an indivisual submission or 
that it is a "00" ID.

(a) ID ACTION is issued only through ietf-announcement list
(b) ID ACTION is issued through both ietr-announcement list and 
     the related WG mailing list.

What differs ? Just curious

Thank you, 

J.