Why do I have to care or think about all the various reasons why IYou don't have to care about why. Or when. You can just handle them as needed.
My use case (which I believe is common): As an owner/moderator, I wantYou will, if you've opted to. The consistency question has to do with "when".
I think the proper way to look at the system behavior is that the +subscribe email user hasn't actually requested to join your group until they respond to the confirmation request from Groups.io.
That point of view is based on the fact that Groups.io ignores any unconfirmed email commands, as if they never happened (except +help and +owner, as mentioned previously). Not only do the group managers not get a notice of a pending member until then, but also the address isn't added to the Pending Members list, nor is the command even logged in the group's Activity log*.
To paraphrase the social media meme, where concerns the email commands like +subscribe: "confirm or it didn't happen".
I'd like to be able to turn these notices off or on at the groupNot sure what you mean by "at the group level".
In each group you own or moderate, you can choose if and how you'll be notified by selecting the desired option for "Pending Members", in the Moderator Notifications panel of your Subscription page in that group.
*I happen to be sympathetic to the notion that failing to even log it may be a problem, notwithstanding the possibility of a spambot flooding the groups's Activity log.