In light of all the confusion on the subject I was wondering if it would be practical for you to set up an auto-forward when transfer receives an Invitation: forward an acknowledgement to the Y!group's -owner address. I know you don't want to reply to the invite, as that would (prematurely) accept the invitation.

A FAQ I'm being asked is whether there's a means other than an Invitation which may be used at Step 1. For example, an email to transfer@groups.io from the moderator's personal email address, including a link to the group or the -subscribe address. Most feel that using their own email service is likely to be more reliable than Y!Groups invite function.