Etiquette Snob here… lol
Generally speaking, the Invites should go out in a timeframe that is AT LEAST 6 to 8 Weeks BEFORE the Wedding (or the Date that you need to make Confirmed Numbers by). As a rule of thumb… 12 Weeks / 3 Months in advance is the usual max.
As far as B-Lists… there is nothing wrong from an Etiquette POV with B-Lists the trick lies in being a good enough Host to manage them effectively… they require extra work, because the important thing, is that NO ONE on a B-List should ever be aware they are (the latest timeframe that a B-List Invite should go out is 3 Weeks before you NEED TO KNOW BY DATE)
Ideally, if you have an A & B-List you are working with 2 Sets of RSVPs, with 2 Different Dates printed on them.
If that isn’t possible (you didn’t think that far ahead when you ordered the RSVPs) then you need to get the A-Listers Invites out with plenty of time to spare… in hopes that the NOs will reply quickly.
The best way to manage an A-List is to send those Invites that are furthest away out first (nothing wrong with mailing out Invites in a staggered fashion, a few everytime you get some done / ready to go… handy too if you plan to do your own Calligraphy).
In this way too… people will receive them over a broader amount of time so there is NO Red Flags that go up that say… that all the A-Listers have theirs… so I must be on the B-List.
As for B-Listers…
Organize your list by Preferance… prioritize who you really really would love to have if you have room.
When the NOs come in… you can send out the Invites in order.
So as to keep a “bit of wiggle space” the rule of thumb for Guests that are replying NO from near (vs far) is that for every NO that comes in you send out half-as-many New Invites from the B-List… just incase anyone calls you back closer to the Wedding to say they’ve made alternate arrangements and are now happy to change their NO to a YES.
So… Say you sent an Invite to Uncle Bob & Aunt Sally… and their kids Robert Jr & Susan. They RSVP with a NO. That is 4 NOs.
You can now issue an Invite from your B-List for 2 People… so your College Roommate Jane and her Hubby Frank.
And you can send it out immediately… no need to wait until all the NOs come in.
Hope this helps,