Yahoo groups are now essentially just E-Mail contact lists. If you are signed up to receive individual e-mails or e-mail digests you will see a copy of anything posted to the group address. Nothing is stored so its sort of "FaceBook lite".
I'm unsure if new members can actually join as all the back end functions seem to have gone dead. Couple of weeks ago a query came up on the old Pratt & Whitney group but I couldn'y get a response sent via the group. Fortunately Yahoo includes personal E-Mail addresses in the header so i went direct.
Seriously kicking myself for not picking up the old Smart & Brown group and porting it over to Groups.io. But I'd just got out from under the Bridgeport Group which was successfully ported by anew management team and didn't want to start over.
Clive